adbtd vs the usual suspects.
where we actually fit.

Mailgun is the canonical multi-tenant transactional ESP. You pay per message ($35/mo for 50k, then $0.80/1k) and you sit on a shared sending pool — your reputation is the average of every other Mailgun customer who happens to share your IP that day. adbtd flips both choices: per-mailbox flat-rate pricing instead of per-message metering, and a dedicated IP from the moment you sign up.

The header difference is concrete. A typical Mailgun message with the default tracked domain shows Return-Path: <bounces+...@mg.your-domain.com> and a DKIM d=mg.your-domain.com — recipients (and inbox-placement classifiers like Gmail's) see the mg. subdomain as a Mailgun-operated identity. With adbtd the same message ships Return-Path: <...@your-domain.com>and d=your-domain.com, no operator subdomain anywhere.

Pricing math at three rough volumes — 50k/mo: Mailgun $35 + dedicated IP $59 = $94 vs adbtd 1 IP + 1 mailbox = $20.99. 200k/mo: Mailgun $155 + IP = $214 vs adbtd same $20.99. 500k/mo: Mailgun ~$395 + IP = $454 vs adbtd unchanged. The break-even where Mailgun becomes cheaper than adbtd is "never" if you only operate one sending domain — adbtd does not meter sends.

Mailgun makes sense if you need their event-webhook tooling and don't care about reputation isolation. adbtd makes sense as soon as deliverability is differentiating, or as soon as you want headers that read like you operate the mailserver yourself.

Postmark is best-in-class for transactional mail and the first place we'd send anyone running a SaaS account-events firehose. They strictly disallow cold outreach and split transactional from broadcast streams. adbtd does not compete in pure transactional — Postmark wins on the SaaS-receipts-and-password-resets workflow.

The most visible Postmark identity leak is the bounce CNAME. Postmark requires you to publish pm-bounces.your-domain.com as a CNAME to pm.mtasv.net; that subdomain then appears in Return-Path on every message. Recipients see pm-bounces.and infer Postmark; spam classifiers see a third-party MTA in the bounce path. adbtd's return-path is just @your-domain.com with no operator subdomain.

Postmark's policy on cold outreach is explicit: their content policy lists "unsolicited email" as grounds for account termination, and broadcast streams have separate rate limits and review. If your use case is agency-style outbound for clients, you cannot realistically run it through Postmark — every campaign risks an account review. adbtd supervises reputation, not content.

Pricing math: Postmark transactional starts at $15/mo for 10k messages and a dedicated IP is $50/mo extra (transactional stream only — broadcast streams cannot have a dedicated IP). 100k/mo lands at $115 + $50 = $165 before any broadcast volume. adbtd at the same volume is $20.99/mo flat with the dedicated IP usable across every domain you own.

Where adbtd diverges: cold outreach at volume (off-limits on Postmark), per-customer IP isolation for agencies running outbound for clients, IMAP mailboxes you can also read in (Postmark is send-only), and per-mailbox pricing instead of per-message.

SendGrid (now Twilio SendGrid) is the legacy ESP with the deepest integration matrix — if every "sign up with email" form you've ever seen has a default ESP, it's SendGrid. The cost is a shared sending pool by default, a dedicated IP only on Pro tier ($89+ /mo plus the IP fee at $80–90/mo), and headers that leak SendGrid identity in several places.

The SendGrid leak surface is wider than Mailgun's or Postmark's. Default messages carry X-SG-EID and X-SG-ID headers (event tracking ids tied to the SendGrid account), the bounce path lands on bounces.sendgrid.net unless Sender Authentication is fully configured, and click-tracking links rewrite through u#######.ct.sendgrid.net. Every one of those is a tell. adbtd ships none of them — no operator headers, no operator bounce host, no operator click-tracking domain.

Pricing math: SendGrid Pro at 100k/mo is $89 base + ~$80 dedicated IP ≈ $169/mo before any IP-warming overhead. adbtd at the same volume on 1 IP is $20.99/mo flat. SendGrid wins above ~1M/mo if you'd otherwise be running multiple IPs and need their event-webhook fanout; below that, adbtd is materially cheaper and isolated.

New SendGrid accounts also go through a manual review, and cold outreach frequently gets accounts reviewed off-platform. adbtd skips the review queue: you get a dedicated IP from minute one and ship under headers that say your domain and only your domain.

SES is the cheapest serious option at scale ($0.10/1k outbound, $0.12/MB of attachments, first 62k/mo free if sent from EC2) and the rawest — you operate the deliverability tooling yourself. Sandbox-by-default, production access requires a support ticket (~24h), no UI for warming, no managed DKIM rotation, no built-in feedback-loop registration with Yahoo / AOL / Outlook.com / Comcast.

The operational footprint to run SES "well" is real work. You configure a custom MAIL FROM domain to avoid amazonses.com showing in Return-Path, set up your own bounce / complaint SNS topics and process them, register for ISP feedback loops by hand, write your own warmup ramp logic, monitor your sending reputation in the SES dashboard, and keep _dmarc + spf aligned across multiple sending identities. Bring-your-own-IP is supported but routes through the AWS BYOIP authorization process and is operationally non-trivial.

Pricing math at 1M/mo: SES is roughly $100 + $24.95 dedicated IP = $125 vs adbtd $20.99. Below 1M/mo, the absolute spread is small enough that operator-time dominates; above 5M/mo, SES is the cost floor and nothing comes close.

adbtd is the managed-service answer for teams who would otherwise build the SES wrapping themselves: dedicated IP issuance, automated SPF / DKIM / DMARC publishing, warmup ramp, FBL handling, postmaster contact provisioning. SES wins on raw cost at scale; adbtd wins on time-to-operational and on agency-style multi-tenancy (each customer their own isolated stack rather than a shared SES account).

Resend is the modern API-first option. Beautifully designed product, fast onboarding, React-Email integration, transactional-and-marketing focus, ToS forbids cold outreach. Currently outbound-only — no IMAP, no inbound to a real mailbox, no per-mailbox identity. The mental model is "API key in, message out", not "operate a mailserver".

Resend's identity leak is the most polite of the bunch — on the Free tier outbound messages carry a "Sent via Resend" footer line, which is removable on Pro+ ($20/mo) along with their click-tracking domain. The DKIM d= aligns to your sending domain on any paid tier. Dedicated IP is Pro+ only at $30/mo extra; the Free and Hobby tiers share IPs. adbtd starts everyone on a dedicated IP, with the customer's domain in every header from day one.

Where Resend is materially better: developer ergonomics for transactional mail, event-webhook fanout, React-Email template rendering, Vercel / Next.js integration. If you are a Next.js startup sending password resets and order confirmations, Resend is probably the right call.

Where adbtd diverges: real Postfix + Dovecot + Rspamd in containers you can read mail on, dedicated IP from the start instead of Pro-tier-only, no per-message metering, and cold outreach permitted on dedicated infrastructure you operate. adbtd is the right pick for an agency or operator who needs an inbox per client and headers that do not say "via Resend".