Postal is a full open-source SMTP server (Postal, 2026). Mailblast is a hosted management layer that uses your own Amazon SES account at $0.10 per 1,000 emails for delivery (AWS, 2026). The comparison isn't tool vs tool - it's build-your-own-email-infrastructure vs use-AWS-infrastructure-with-a-UI-on-top. Both can move bulk email, but the operational, financial, and deliverability shapes are different by an order of magnitude.
This post walks through what Postal actually is, where the work lives in each model, and which option is the right call for which kind of sender.
What Postal Actually Is
Postal is a complete Mail Transfer Agent, not just an ESP frontend. The project has 16,600 stars on GitHub, ships under the MIT license, and is built on Ruby on Rails with MariaDB and RabbitMQ as required dependencies (Postal, 2026). It speaks SMTP in both directions - sending campaigns and receiving inbound mail, bounces, and FBL reports - and includes IP pool management, click and open tracking, webhooks, and a multi-tenant web UI for managing multiple sending domains.
Functionally, Postal is closest to "self-hosted Mailgun." If Mailgun, SendGrid, and Amazon SES are the managed versions of this category, Postal is the version you install on your own Linux box. That places it in a different category from Mailblast, which is a marketing UI layered over AWS's sending infrastructure. Conflating the two understates what running Postal commits you to: you become the mail provider, not the mail customer.
Architecture: Self-Hosted MTA vs Managed Delivery
The architectural split decides almost every downstream difference. Postal runs on infrastructure you own and operate. A minimal production install is one or more Linux servers with at least 4 GB of RAM, MariaDB or MySQL, RabbitMQ for queueing, a static public IPv4 address with reverse DNS that you control, and outbound port 25 open from your provider. Most cloud providers either block port 25 by default or charge extra to unblock it, which narrows host choice early.
Mailblast doesn't run on infrastructure you operate at all. The management UI is hosted by Mailblast, and the actual SMTP transmission happens inside AWS SES under your AWS account. You bring AWS credentials; AWS handles the mail servers, IP pools, queueing, and FBL plumbing; AWS bills you per email. Your responsibility ends at DNS records (SPF, DKIM, DMARC) and AWS account hygiene.
For a head-to-head on the underlying engines, see Amazon SES vs Postal. The short version is that AWS SES has been operating shared and dedicated IP pools for over a decade and has direct Postmaster relationships at Google, Microsoft, and Yahoo. A fresh Postal install has none of that.
Deliverability Ownership: The Hidden Cost of Self-Hosted SMTP
When you self-host an MTA, you also self-host deliverability. M3AAWG's Sender BCP guidance emphasizes that legitimate bulk senders need warmed IPs, monitored complaint rates under 0.1%, working feedback loops with every major mailbox provider, and rapid response to reputation signals (M3AAWG, 2015). On AWS SES that work is mostly automated - SES exposes bounce and complaint metrics, feeds back into your CloudWatch alerts, and will pause sending if you cross AWS's reputation thresholds (AWS, 2026). On a fresh Postal install it is yours from day one.
The practical implication: a brand new Postal deployment on a brand new IP starts at zero reputation. Gmail and Outlook treat unknown IPs sending high volume as suspicious by default. Warming a single IP from zero to 100,000 emails per day takes two to four weeks of carefully ramped volume with clean engagement signals. If you misjudge the ramp, you collect spam-folder placements or, worse, an IP block that takes weeks of remediation to unwind.
The reputation column is the one most underestimated by first-time self-hosters. With Mailblast on AWS SES, a deliverability incident usually means an AWS reputation warning that's resolved by tightening your list. With Postal, the same incident can mean your IP lands on Spamhaus or UCEPROTECT and you spend a week filing delisting requests and explaining your sending practices to a volunteer admin.
Cost Reality: License vs Subscription vs Total Infrastructure
Postal's software is free. Running it is not. A realistic minimum production deployment is one application server (~$20-40 per month), a managed database for MariaDB (~$25-50 per month), and a queue broker for RabbitMQ if you don't co-locate it (~$15-30 per month). Add a static IP with reverse DNS, monitoring, and backups, and the floor is around $60-120 per month for infrastructure alone, before any operator time.
Mailblast is $0 up to 1,000 contacts and 10,000 emails per month, then $10 per month for that same 1,000 contacts on the smallest paid plan. AWS SES is $0.10 per 1,000 emails on top. At 100,000 emails per month (10,000 contacts, $20/month on Mailblast's ladder) SES adds $10. The total at 100k emails per month: roughly $30 with Mailblast plus AWS, versus roughly $80-120 of infrastructure with Postal before any operator hours.
The math flips only at large volume. If you're sending 5 million emails a month, the Postal infrastructure floor is similar but AWS SES adds $500, narrowing the gap. At 20 million per month, the AWS bill alone is $2,000 and the Postal infrastructure is still ~$200 plus operator time - that's where the case for self-hosting actually starts to hold up, but only if the operator time is already covered by an in-house mail team.
Postal vs Mailblast: Side-by-Side
| Dimension | Postal | Mailblast |
|---|---|---|
| Category | Open-source SMTP server / MTA | Hosted management layer on Amazon SES |
| License / pricing | MIT, free software | Free up to 1,000 contacts; from $10/month |
| Sending infrastructure | Your own servers and IPs | Amazon SES under your AWS account |
| Stack you operate | Ruby on Rails, MariaDB, RabbitMQ, Linux | None on your side |
| Inbound mail handling | ✓ Yes (full MTA) | ✗ No (outbound marketing only) |
| Drag-and-drop editor | ✗ No (API/SMTP only) | ✓ Yes (BeeFree-powered) |
| Subscriber lists & segmentation | ✗ No (you wire your own) | ✓ Yes |
| Automation / drip campaigns | ✗ No | ✓ Yes (on all plans, including free) |
| Click and open tracking | ✓ Yes | ✓ Yes |
| IP reputation on day one | Zero (build from scratch) | Inherits AWS SES pool reputation |
| Feedback loop integration | Manual per mailbox provider | Managed via AWS SNS feedback |
| Server uptime monitoring | Your responsibility | Not applicable |
| Multi-brand / multi-tenant | ✓ Yes | ✗ No (single-brand) |
| Realistic monthly TCO at 100k emails | $80-120 infra + 6+ hours ops | ~$30 total, <1 hour ops |
The blank cells for editor, lists, and automation under Postal are not failings - they reflect that Postal isn't trying to be a marketing platform. It's the engine. To send marketing campaigns through Postal you bolt a list manager (often listmonk or a custom Rails app) onto its API. Mailblast bundles the engine (AWS SES) with the marketing layer, so there's nothing to bolt on.
When Postal Is the Right Call
Postal is the right tool in a specific set of situations. The clearest case is when you also need to receive mail at scale - transactional inbound, parsed forwarding, or running mailboxes for an internal product. AWS SES can receive mail too, but Postal handles inbound natively as part of the same server, and the integration with custom webhook routing is more flexible.
A second case is regulatory or data residency. If your contract or jurisdiction prohibits sending customer data through AWS - some EU public sector and healthcare deployments fall here - self-hosted Postal on EU infrastructure you control is a defensible answer that AWS SES isn't.
A third case is scale plus existing mail ops. If you're already sending 10 million emails a month, already have an SRE who understands SMTP, BGP, and DNS at depth, and already maintain abuse@ desks and FBL parsers, the marginal cost of adding Postal to that team is lower than the AWS bill at that volume. This is rare.
The case where Postal does not pay back is "we wanted to save money on sending." The savings on the AWS bill are eaten by infrastructure plus operator hours within months, and the deliverability risk during IP warmup can dwarf both.
When Mailblast Is the Right Call
For everyone who isn't in one of the three Postal scenarios above, Mailblast is the better answer. You get the BeeFree drag-and-drop editor, list management, automation including welcome sequences and drip campaigns on every paid plan, bounce and complaint handling, and AWS SES's mature deliverability infrastructure - without owning a Rails server, a MariaDB cluster, a RabbitMQ broker, or a Linux box with port 25 open.
The free plan covers 1,000 contacts and 10,000 emails per month with no automation sends; paid plans start at $10 per month for that same 1,000 contacts and add automation plus unbranded sending. For senders coming from a self-hosted PHP tool, the same logic applies in the Sendy vs Mailblast head-to-head: you keep your AWS sending costs and shed the server.
If your goal is to send newsletters, marketing campaigns, or product updates to a list of subscribers with clean deliverability and predictable cost, Mailblast on AWS SES is the more efficient choice. The operational pattern holds consistently: managed delivery beats self-hosted SMTP for almost every sender below the eight-figures-per-month mark.
FAQ
Is Postal free and Mailblast paid?
Postal's software is free under the MIT license, but running it is not. You pay for a Linux server (typically two or more, plus a database host), a static IP with reverse DNS, MariaDB and RabbitMQ resources, and your own operator time. Mailblast has a free plan up to 1,000 contacts and paid plans from $10 per month, and uses Amazon SES at $0.10 per 1,000 emails for sending.
What is Postal exactly?
Postal is an open-source full mail server, similar in scope to Mailgun or SendGrid but installed and operated by you. It speaks SMTP both ways - sending and receiving - and includes IP pools, click and open tracking, webhooks, and a multi-tenant web UI. It is a Mail Transfer Agent, not a frontend on top of someone else's infrastructure.
Does Postal have better deliverability than Amazon SES?
No. Deliverability depends on the IP's reputation with major mailbox providers, and on a fresh self-hosted Postal install you start at zero. Amazon SES has been operating shared and dedicated IP pools for over a decade with established reputation, automated bounce and complaint feedback loops, and direct Postmaster relationships. Mailblast inherits that.
Can Mailblast import data from Postal?
Mailblast accepts CSV imports of subscribers, lists, and segments, which covers the migration path from Postal's message logs and any subscriber data you've stored alongside it. Postal is a sending engine, not a marketing platform, so most operators run a separate list manager in front of it - that's typically the source data for the move.
When does running Postal actually make sense?
When you have an in-house mail operations team, need to receive mail as well as send it, are bound by data residency rules that prohibit AWS, or are sending at a volume where building IP reputation in-house pays back the infrastructure cost. For everyone else, using AWS SES through a managed layer like Mailblast is faster and more reliable.
Disclosure: Mailblast is the product behind this blog. This comparison reflects how we see the trade-offs; we've tried to represent Postal accurately based on its public documentation and source.