ChatGPT answers, unedited

For low-volume but important transactional email, I’d put Brevo at the top of the list if you want one platform to handle both marketing and transactional mail.

Brevo supports marketing campaigns and transactional email through its API or SMTP relay. Its free plan currently includes 300 emails/day, including transactional email, and paid plans start at $9/month. help.brevo.com

My shortlist

Why I'd choose Brevo

The important distinction is that your transactional messages shouldn't simply be sent as ordinary marketing campaigns. Brevo has a dedicated transactional service, with SMTP/API sending, templates, delivery tracking, and transactional logs. help.brevo.com

For example, you could use the same account/domain infrastructure for:

• Marketing newsletters
• Product announcements
• Password resets
• Account verification
• Order/invoice confirmations
• Important system notifications

And at low volume, the free 300/day allowance may be enough without paying anything. help.brevo.com

One important caveat

Because the transactional mail is important, I'd configure it with proper domain authentication (SPF/DKIM) and keep marketing and transactional streams logically separated—ideally with different sending addresses/subdomains. Brevo specifically requires domain authentication as part of setting up transactional sending. help.brevo.com

If by "important" you mean mission-critical (e.g., password resets, financial receipts, security alerts), I'd actually consider Brevo for marketing + a dedicated transactional provider such as SES/Postmark/Resend rather than putting everything on one provider. The extra separation can protect transactional deliverability if a marketing campaign ever causes reputation problems.

Bottom line: For low volume + low cost + one platform, Brevo is probably the sweet spot. For maximum transactional reliability, I'd separate the two streams.

For a low-volume but important transactional email requirement, I would prioritize deliverability isolation and reliability over having the cheapest per-email price. The best budget-friendly choice depends on how important those transactional messages are.

Best overall fit: Brevo

Best if you want one platform for both marketing + transactional email

• ✅ Marketing campaigns, newsletters, automation, and transactional API/SMTP in one account
• ✅ Low cost at small volumes
• ✅ Easier for non-developers than developer-only providers
• ⚠️ The main risk: marketing and transactional traffic can share reputation/infrastructure, so a poorly performing marketing campaign can potentially affect deliverability. lettr.comwww.sequenzy.com

For a small business sending things like:

• password resets
• account confirmations
• invoices/receipts
• appointment notifications

…but also newsletters and campaigns, Brevo is usually the pragmatic budget choice. lettr.comwww.sequenzy.com

Best if transactional emails are truly mission-critical: Postmark

Best for “this email must arrive” use cases

• ✅ Strong transactional focus
• ✅ Better separation between transactional streams and other mail
• ✅ Excellent logs/debugging for individual messages
• ❌ More expensive because you may still need a separate marketing platform

For things like:

• payment failures
• security alerts
• login codes
• critical workflow notifications

I would lean Postmark and keep marketing elsewhere. coldletter.com

Best developer-friendly budget option: Resend

• ✅ Modern API and developer experience
• ✅ Good for application-triggered email
• ✅ Low-volume pricing is attractive
• ⚠️ Marketing features are newer/less mature than dedicated marketing platforms coldletter.com

Cheapest at scale: Amazon SES

• ✅ Extremely low sending cost
• ✅ Good if you already run on AWS
• ❌ Requires more engineering: templates, suppression handling, monitoring, reputation management lettr.com

My recommendation for your scenario

For low volume + important transactional + wanting marketing in the same place:

1. Brevo → best balance of cost and simplicity
2. Resend + a marketing platform → best technical architecture
3. Postmark + marketing platform → best reliability, higher cost
4. Amazon SES → only if you have engineering time and want minimum cost

One architectural suggestion: even if you use a single vendor, create separate sending identities:

• mail.yourdomain.com or tx.yourdomain.com → transactional
• news.yourdomain.com → marketing

Use separate DKIM/SPF alignment and avoid sending bulk campaigns from the same stream as password resets or receipts. That separation matters more than the vendor choice for protecting deliverability. lettr.com

For low-volume but business-critical transactional email, my first choice would be brevo.com.

Why it fits particularly well:

• One platform for both marketing + transactional: Brevo's free tier explicitly includes both marketing campaigns and transactional email. Brevo Help
• Very inexpensive at low volume: the current free plan allows 300 emails/day, with paid plans starting around $9/month. Brevo Help Brevo
• Transactional API/SMTP: you can trigger password resets, receipts, confirmations, etc. programmatically rather than treating them as marketing campaigns. Brevo
• Shared IPs are actually appropriate for low volume. Brevo specifically says shared IPs are suitable for senders doing only hundreds or thousands of emails periodically; dedicated IPs aren't recommended until you're sending substantially more. Brevo Help Brevo Help
• You can use separate sender identities/domains for marketing versus transactional mail, which I'd recommend even if you're on the same account. Brevo supports separate routing when you eventually need stronger isolation. Brevo Help

The important caveat

If the transactional messages are mission-critical—e.g. login codes, payment confirmations, account recovery, or legally important notifications—I would not simply blast marketing and transactional mail through the exact same sender/domain reputation.

I'd configure something like:

• news@marketing.example.com → marketing
• notifications@transactional.example.com → transactional
• SPF + DKIM + DMARC on the relevant domains/subdomains
• Keep transactional sending strictly opt-in/triggered and never mix promotional content into it.

At your volume, don't buy a dedicated IP just for this. Brevo itself recommends dedicated IPs primarily for senders doing 100,000+ emails/month or frequent campaigns to thousands of recipients. Brevo Help

What about MailerSend?

mailersend.com is another strong option if the transactional side is more important than the marketing side. It can be managed through the same account as MailerLite, and currently starts around $7/month. MailerLite

But for your particular requirement—one budget-friendly platform where marketing and transactional sending coexist—I'd pick Brevo.

If you tell me roughly how many transactional emails/month and marketing emails/month you expect, I can compare Brevo vs MailerSend/MailerLite vs Amazon SES/Resend and identify the cheapest safe architecture.

For your use case, I’d pick Brevo (formerly Sendinblue).

Why it fits particularly well:

• One platform for both marketing and transactional email. Brevo explicitly supports campaigns plus transactional messages through its API or SMTP relay. help.brevo.com
• Very cheap at low volume: the free tier allows 300 emails/day and includes transactional email, marketing campaigns, and API/SMTP access. help.brevo.comwww.brevo.com
• Easy upgrade path: Starter begins at about $9/month for 5,000 emails/month. help.brevo.com
• Appropriate infrastructure for important transactional mail: it supports SPF/DKIM/DMARC, bounce/suppression handling, tracking, SMTP and API delivery. help.brevo.comwww.brevo.com
• Its send-based pricing is attractive if you have a relatively large marketing list but send infrequently.

My ranking

One important distinction: MailerLite itself isn't the transactional product; its transactional offering is MailerSend, although the two can be managed under one account. MailerSend currently advertises 500 free transactional emails/month and plans starting at $7/month. help.brevo.comwww.mailerlite.com

What I'd do

If the transactional emails are genuinely important—password resets, invoices, account verification, critical notifications, etc.—I'd use Brevo with separate sending identities/subdomains for marketing and transactional mail, e.g.:

• marketing.example.com → newsletters/promotions
• notify.example.com → transactional mail

That gives you the convenience and cost savings of one provider while reducing the risk that marketing activity affects the reputation of your important transactional stream.

Bottom line: Brevo is probably the sweet spot for "small volume + important transactional + some marketing + don't want two vendors." Its free tier is unusually well suited to this scenario. help.brevo.com

Brevo official site

For your use case, Brevo is probably the best budget-friendly choice.

Brevo supports both marketing campaigns and true transactional email through its API/SMTP, so you don't need two vendors. help.brevo.com

Why I'd pick Brevo

• Low cost: the free tier includes 300 emails/day and supports both marketing and transactional email. Paid Starter begins around $9/month. help.brevo.com
• Transactional API/SMTP: appropriate for password resets, receipts, notifications, account emails, etc. help.brevo.com
• Marketing functionality: campaigns, contact management, segmentation, automation, templates, etc.
• Pay-as-you-go option: particularly attractive if your volume is low; prepaid credits don't expire and can be used for both marketing and transactional sends. help.brevo.com
• One important caveat: because your transactional mail is important, I'd keep the transactional and marketing sender identities/subdomains separate (e.g. notify.example.com vs. news.example.com). Brevo itself recommends separating routing when protecting transactional deliverability matters. help.brevo.com

Runner-up: MailerLite + MailerSend

MailerLite is excellent for marketing, while its sister product MailerSend handles transactional mail. MailerSend starts at $7/month and explicitly supports using one account/SSO for both. www.mailerlite.com

But that's effectively two products, so I'd choose Brevo if minimizing cost and operational complexity is the priority.

Bottom line: For low volume + important transactional emails + marketing in the same platform, I'd start with Brevo, configure authenticated sending (SPF/DKIM), and use a dedicated transactional subdomain. If the transactional messages become truly mission-critical at larger scale, I'd consider splitting them to a specialist such as Postmark while retaining Brevo for marketing.

For your use case, Brevo is probably the best budget-friendly choice.

Brevo supports both marketing campaigns and transactional email in the same account, including API/SMTP transactional sending. Its free tier currently includes 300 emails/day, and the Starter plan begins at $9/month for 5,000 emails/month. help.brevo.comwww.brevo.com

Why I'd pick Brevo

Brevo is particularly attractive because its email credits can explicitly be used for both marketing and transactional messages, rather than forcing you into two separate products. help.brevo.com

One important caveat: because the transactional mail is important, don't treat it exactly like marketing mail. I'd configure SPF, DKIM and DMARC, use a dedicated transactional subdomain such as mail.example.com, and keep promotional content out of transactional templates. Brevo supports those authentication mechanisms and suppression/bounce handling. help.brevo.comwww.brevo.com

If your volume is really low—say a few hundred transactional emails/month plus occasional newsletters—I'd start on Brevo's free tier and only upgrade when the 300/day limit becomes relevant.

A close second is MailerLite + MailerSend: they now offer a unified account, with MailerSend handling API/SMTP transactional mail and MailerLite handling marketing. help.brevo.comwww.mailerlite.com But for your requirement of keeping things simple and inexpensive, Brevo wins.

For a low-volume but important transactional email requirement, I would be cautious about putting everything into a typical marketing-first platform. The key risk is reputation and traffic separation: a newsletter campaign with complaints or a bad list can hurt password resets, receipts, alerts, or other critical messages if they share sending infrastructure. lettr.com

My shortlist:

My recommendation by scenario

1. You want one budget-friendly platform for both marketing + transactional
→ Brevo is probably the pragmatic choice. It is designed for this exact use case and is inexpensive for low volumes. mailtrap.iocoldletter.com
Use a separate transactional subdomain, for example:

• notify.example.com → receipts, account alerts, password resets
• news.example.com → newsletters and promotions

Configure SPF, DKIM, and DMARC correctly for both.

2. Your transactional emails are business-critical
→ Use Postmark (transactional) + a cheaper marketing ESP. The extra cost buys cleaner separation and better operational focus. lettr.comcoldletter.com

3. You send only a few thousand transactional emails/month and have developers
→ Resend is a strong middle ground: low cost, modern API, and easier than AWS SES. www.stackscored.comcoldletter.com

What I would avoid

I would avoid making a marketing-only tool the sole home for critical transactional messages unless it has:

• separate transactional streams/domains
• good bounce/suppression handling
• API-based sending
• delivery logs
• strong authentication support (SPF/DKIM/DMARC)

For a small company, my default choice would be:

• Brevo if you truly want one tool.
• Postmark + your existing marketing tool if those transactional emails affect revenue, access, or customer trust.
• Resend if this is an app/product with a technical team. www.stackscored.comcoldletter.com

For your use case, Brevo would be my first choice.

Brevo is unusually well-suited to low-volume but important transactional email + marketing email in one account:

• Free tier: 300 emails/day, including both marketing and transactional sending. help.brevo.com
• Transactional API + SMTP: suitable for password resets, receipts, account notifications, etc. help.brevo.com
• Marketing campaigns: newsletters, automations, contact management, templates, etc. are built into the same platform. help.brevo.com
• Low cost to grow: Starter starts at $9/month for 5,000 emails, with transactional and marketing sends covered. help.brevo.com
• It supports proper SPF/DKIM/DMARC authentication and suppression/bounce handling, which matters considerably when the transactional messages are business-critical. www.brevo.com

One important caveat

I would not treat "one platform" as meaning "one undifferentiated sending stream." Your transactional mail is more important than your marketing mail. Poor marketing engagement can potentially hurt the reputation of the infrastructure/domain used for important notifications.

So I'd set it up with:

Marketing: news.example.com or marketing.example.com
Transactional: notify.example.com / mail.example.com

and authenticate the sending domains properly. Keep transactional templates, lists, and sending logic separate from promotional campaigns.

What about MailerLite?

MailerLite is attractive for marketing, and its ecosystem now includes MailerSend for transactional mail, with a single account/SSO experience. help.brevo.comwww.mailerlite.comwww.mailerlite.com But that effectively means a separate transactional product, and MailerLite itself explicitly recommends separating transactional and marketing email for deliverability reasons. www.mailerlite.com

Bottom line: if you specifically want one inexpensive vendor/account that can handle both, I'd choose Brevo. For low volume, you can start at $0 and only pay when your needs grow. help.brevo.com

Brevo official site

If you tell me roughly how many transactional emails/month and marketing emails/month you expect, I can also compare Brevo vs Postmark + a marketing platform, MailerLite/MailerSend, Resend, and Amazon SES specifically for reliability and cost.

For low-volume but business-critical transactional email, while also wanting marketing email in the same platform, my first choice would be Brevo.

Why Brevo is the best budget fit

• One platform for both: Brevo explicitly supports both marketing campaigns and transactional email, including using the same email credits for both. help.brevo.com
• Very inexpensive at low volume: the free tier allows 300 emails/day, including transactional sends. The Starter plan starts at $9/month for 5,000 emails/month. help.brevo.com
• Proper transactional infrastructure: you can send critical messages through their SMTP relay or API, rather than treating them like ordinary marketing campaigns. help.brevo.com
• Good fit for a small operation: you get contact management, templates, analytics, automation, and marketing tools without paying for a separate transactional provider. help.brevo.com

The important caveat: don't simply throw marketing and transactional mail into the exact same sending stream. Brevo itself recommends separating the routing of transactional and marketing email because poor marketing engagement can hurt the deliverability of critical messages. help.brevo.com

I'd therefore set it up roughly as:

Marketing: news@yourdomain.com → Brevo campaigns
Transactional: notifications@yourdomain.com or system@yourdomain.com → Brevo SMTP/API
Authentication: SPF + DKIM + DMARC
Transactional: separate sender/routing from marketing

How I'd rank the alternatives

MailerSend, which is part of the MailerLite ecosystem, starts at $7/month and has strong API/SMTP transactional capabilities, but the separation makes it less attractive if your goal is one inexpensive platform. help.brevo.comhelp.brevo.comhelp.brevo.comhelp.brevo.comwww.mailerlite.com Mailgun is stronger if transactional reliability/developer tooling is the dominant concern, but its paid plans start around $15/month for 10,000 emails. www.mailgun.com

Bottom line: for something like a few hundred/thousand marketing emails plus occasional password resets, receipts, confirmations, alerts, etc., I'd choose Brevo. For the transactional side, I'd still configure it as a distinct sender/stream and authenticate the domain properly.

Brevo official site 

For a low-volume but business-critical transactional email requirement, I would usually avoid putting all trust into a pure marketing platform unless it has a strong transactional email product. The main risks are:

• marketing campaigns hurting your sender reputation
• a marketing account suspension affecting password resets/order confirmations
• weaker API/webhook tooling
• less control over deliverability

For a budget-conscious setup where you want one platform for both marketing + transactional, the strongest candidates are:

My recommendation for your scenario

Pick Brevo if:

• you send fewer than ~50k emails/month
• you want one dashboard
• your transactional emails are important but not mission-critical at massive scale
• you want low operational overhead

Brevo’s free tier includes transactional email capability, and paid plans start at low monthly costs; it supports SMTP/API sending alongside marketing campaigns. help.brevo.comwww.brevo.com

How I would structure it safely

Even with an all-in-one platform:

1. Use separate sender identities
   • Marketing: news@yourdomain.com
   • Transactional: notify@yourdomain.com or no-reply@yourdomain.com

2. Authenticate your domain
   • SPF
   • DKIM
   • DMARC

3. Keep transactional templates isolated
   • no promotional content
   • no marketing footers
   • minimal links

4. Monitor transactional delivery separately
   • bounce rate
   • spam complaints
   • failed sends
   • delivery latency

5. Have a fallback plan
   • Export templates/API keys/configuration
   • Know how quickly you could move transactional sending to another provider

When I would not combine them

If the transactional emails are things like:

• password resets
• 2FA codes
• payment receipts
• legal notices
• account access alerts

…I would lean toward separating them: use a transactional specialist such as SES, Postmark, or Mailgun, and keep marketing elsewhere.

For a small SaaS, membership site, nonprofit, or service business, though, Brevo is probably the best balance of cost, simplicity, and acceptable risk. help.brevo.comwww.brevo.com

For low volume + important transactional email + marketing in one platform, I’d shortlist Brevo first, with MailerLite/MailerSend as the budget alternative.

My pick: Brevo

Brevo is probably the best fit if you want one inexpensive system rather than stitching together a marketing ESP and a transactional provider.

• Free tier: 300 emails/day, including both marketing campaigns and transactional email. help.brevo.comwww.brevo.com
• Transactional API/SMTP: included, so your app can send password resets, receipts, notifications, etc. help.brevo.comwww.brevo.com
• Low-volume shared IPs are actually appropriate: Brevo says shared IPs are suitable for senders doing a few hundred/thousand emails periodically, whereas dedicated IPs are intended for much higher volume. help.brevo.com
• You can use different senders/subdomains for marketing vs. transactional, which is important for protecting the reputation of your critical mail. help.brevo.com

The important caveat: don't treat "one platform" as "one undifferentiated email stream." I'd configure something like:

• news.example.com → marketing
• notify.example.com → transactional
• SPF + DKIM + DMARC properly configured
• separate From addresses
• transactional messages excluded from marketing unsubscribe/suppression logic

At your low volume, I would not buy a dedicated IP. Brevo itself recommends shared IPs for low-volume senders. help.brevo.com

Runner-up: MailerLite + MailerSend

MailerLite is attractive if your marketing needs are especially simple. Its transactional product, MailerSend, starts at $7/month and the company explicitly supports managing marketing and transactional email under one account. www.mailerlite.com

The distinction is that MailerSend is essentially the transactional side of the MailerLite ecosystem, whereas Brevo feels more like a single unified platform.

What I would avoid for your particular requirement

SendGrid is technically excellent and supports marketing + transactional from one account. sendgrid.com But there's an important wrinkle: SendGrid explicitly warns that its low-cost shared IP pools are poorly suited to critical transactional messages, because other senders' marketing reputation can affect them. support.sendgrid.com Their own guidance recommends separating transactional and marketing streams onto different IPs as you become more significant. sendgrid.com

So for "cheap, low volume, but these transactional emails really matter", I'd rank them:

Bottom line: I'd start with Brevo's free tier, authenticate your domain, and keep marketing and transactional mail on separate subdomains/senders. If your transactional mail is truly business-critical (password resets, payments, security alerts), that separation matters more than paying for a premium marketing platform. Brevo specifically documents separate routing for marketing vs. transactional mail for this reason. help.brevo.com

If you tell me roughly how many marketing emails/month and transactional emails/month you expect, I can give you the cheapest 2–3 setups and estimated monthly cost.

For low-volume but business-critical transactional email, I’d shortlist Brevo first, with MailerLite + MailerSend as the other strong budget option.

My pick: Brevo

Brevo is probably the best fit if you want one platform for both marketing and transactional email without paying for a high-end ESP.

Why:

• Marketing + transactional in one account. Brevo supports normal campaigns/automations plus transactional email through its API or SMTP relay. help.brevo.com
• Good fit for low volume. You don't need to maintain a dedicated IP at your volume; Brevo itself recommends shared IPs when you can't maintain the consistent volume needed to establish a dedicated-IP reputation. help.brevo.com
• Transactional API/SMTP is mature. You can send password resets, receipts, account notifications, etc. through SMTP or the API. developers.brevo.com
• You can separate marketing and transactional identities. Even if you remain on shared infrastructure, I'd use distinct senders/subdomains—for example news@marketing.example.com and notifications@tx.example.com. Brevo explicitly recommends separating the streams when deliverability of transactional mail is particularly important. help.brevo.com

Runner-up: MailerLite + MailerSend

MailerLite has a particularly clean arrangement: MailerLite handles marketing while MailerSend handles transactional, with both accessible under the same account/SSO. MailerSend starts at $7/month according to its current pricing information. www.mailerlite.com

I'd choose this combination if your marketing requirements are primarily newsletters, simple automations, and audience management and you want the transactional system to be more explicitly separated.

The important caveat

If the transactional emails are truly critical—password resets, payment confirmations, security notifications, etc.—I wouldn't simply throw marketing and transactional mail onto the same sending identity. Marketing complaints/unsubscribes can hurt the reputation that your transactional mail depends on. Brevo specifically notes this risk. help.brevo.com

A sensible low-volume architecture is:

Marketing: news@marketing.example.com
↓
marketing platform

Transactional: notifications@tx.example.com
↓
transactional API/SMTP

Same provider/account is fine; separate sender/subdomain and authenticated DNS is the part I'd prioritize.

Bottom line: If you want one inexpensive platform, I'd go Brevo. If you're comfortable with a closely integrated two-product setup, MailerLite + MailerSend is also compelling.

If you tell me roughly how many marketing emails/month and transactional emails/month (e.g. 500 + 2,000), I can compare the current costs and limits of Brevo, MailerLite/MailerSend, SendGrid, Amazon SES, and Postmark for your exact volume.

For your use case, Brevo is probably the best budget-friendly choice.

• One platform for both: Brevo supports marketing campaigns and transactional email via API/SMTP. help.brevo.comwww.brevo.com
• Very low cost: its free tier includes 300 emails/day and transactional sending; paid plans start at $9/month. help.brevo.com
• Low-volume sending actually fits its shared infrastructure: Brevo says shared IPs are appropriate for senders doing only a few hundred/thousand emails periodically, whereas dedicated IPs are aimed at much higher volumes. help.brevo.comhelp.brevo.com
• Good transactional tooling: API/SMTP, webhooks, bounce/suppression handling, SPF/DKIM/DMARC support, and delivery analytics are available. help.brevo.comwww.brevo.com

The important caveat

If the transactional messages are business-critical—password resets, invoices, account alerts, order confirmations, etc.—I would not simply mix marketing and transactional traffic on the same sender identity.

Use separate subdomains, for example:

• news.example.com → marketing
• mail.example.com → transactional

And ideally use distinct sender addresses such as newsletter@... and notifications@....

Brevo itself recommends separating marketing and transactional traffic when deliverability is particularly important, because poor engagement or complaints on marketing mail can hurt transactional delivery when the traffic shares infrastructure. help.brevo.com

For low volume, though, I would not pay for a dedicated IP. Brevo specifically says dedicated IPs are intended for roughly 100,000+ emails/month or frequent campaigns to 3,000+ contacts; a shared IP is generally more appropriate below that. help.brevo.comhelp.brevo.com

My pick: Brevo, with marketing and transactional mail separated by sender/subdomain. It's one of the cleaner ways to avoid paying for two separate services while keeping the important transactional stream reasonably protected.

A good alternative is MailerSend + MailerLite, which now supports managing marketing and transactional email under one account, starting at $7/month for the transactional side. www.mailerlite.com But if minimizing complexity and cost is the priority, I'd start with Brevo.

For low-volume but business-critical transactional email, I’d put Brevo at the top of the list.

Brevo

Why Brevo fits particularly well

• One platform for both jobs: Brevo explicitly separates marketing campaigns from transactional sending, while supporting both under the same account. help.brevo.com
• Very inexpensive at low volume: its current Free plan is $0 and includes 300 emails/day, including transactional email. The Starter plan begins at $9/month if you need more sending capacity. help.brevo.com
• Proper transactional infrastructure: you can send through an API or SMTP relay, rather than trying to repurpose a marketing-campaign mechanism. help.brevo.com
• Good operational visibility: transactional delivery, bounce, click, complaint, unsubscribe and other events can be tracked, including via webhooks. developers.brevo.com
• Domain authentication: Brevo recommends authenticating your sending domain before enabling transactional sending, which is important when the messages actually matter. help.brevo.com

The important caveat

I wouldn't treat marketing and transactional mail as literally the same stream just because they're on the same provider.

For example:

Marketing:
news@yourdomain.com → newsletters, promotions, announcements

Transactional:
notifications@yourdomain.com → password resets, invoices, account alerts

Use separate sender identities/subdomains if the transactional messages are genuinely important. That way, a marketing-list problem or campaign complaint is less likely to jeopardize the reputation of the mail that users depend on.

For a small SaaS, membership site, nonprofit, or business application, my architecture would be:

Brevo + authenticated domain + separate transactional sender/subdomain + API/SMTP for application mail + Brevo campaigns for marketing.

That's a much better fit than using a marketing-only platform for transactional messages. Brevo's API supports dynamic transactional content and delivery-event webhooks, too. developers.brevo.com

If you tell me roughly how many marketing emails/month and how many transactional emails/month, I can compare Brevo vs MailerLite vs Mailchimp vs SendGrid/Postmark specifically for your volume and reliability requirements.

For low-volume but business-critical transactional email, I’d pick Brevo if you want one budget-friendly platform for both marketing and transactional mail.

My ranking

Why Brevo stands out: its free plan currently includes both marketing campaigns and transactional email, with 300 email sends/day. Its paid Starter plan begins at $9/month, and transactional email has API/SMTP access. help.brevo.com

The important caveat is deliverability isolation. I would not casually put mission-critical password resets, invoices, or account notifications on exactly the same sending identity as promotional campaigns. Brevo itself recommends separating marketing and transactional routing when deliverability is important, because poor engagement, unsubscribes, and complaints from marketing mail can affect transactional delivery when they share infrastructure. help.brevo.com

For a low-volume setup, though, you generally don't need a dedicated IP. Brevo says dedicated IPs are more appropriate at substantially higher volumes (e.g. >100,000 emails/month or frequent campaigns to thousands of contacts). help.brevo.com

The setup I'd use

• Marketing: news@marketing.yourdomain.com
• Transactional: account@transactional.yourdomain.com
• Authenticate your domain with SPF + DKIM + DMARC
• Keep transactional templates strictly transactional—no promotional content
• Maintain separate suppression/unsubscribe logic for marketing
• Monitor bounces, complaints, and delivery separately

Bottom line: For your described use case, Brevo is probably the sweet spot: inexpensive, one platform, API/SMTP transactional support, and marketing tools included. If the transactional emails are extremely business-critical (e.g. authentication codes or legally important notices), I'd consider a dedicated transactional provider alongside your marketing platform rather than optimizing for having literally everything under one roof.

Mailchimp is less attractive for this particular requirement: its transactional service is an add-on to Standard/Premium, with transactional credits starting at $20 per 25,000 emails, on top of the marketing plan. help.brevo.commailchimp.com