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Guides File 029

Deliverability

What delivers Postboi's mail (Amazon SES in the EU), how your domain is authenticated, and what we do to keep sending reputation clean, from warm-up limits to nightly blocklist checks.

Deliverability is whether mail reaches the inbox, and it rests on three things: the infrastructure it leaves from, the authentication on the domain it claims to be from, and the reputation of everyone sending beside you. This page is what Postboi does about each. How it’s going is measured, not claimed: the delivery record publishes how fast our mail reaches Gmail, Outlook, Yahoo and iCloud, and our uptime, from our own sends.

What delivers it

Postboi’s own sending is delivered by Amazon SES in the EU (Stockholm, eu-north-1). We don’t run our own mail servers; SES is the delivery layer under Postboi’s API, message log, webhooks and suppressions, the same way it sits under a good share of the email industry.

  • Each team is its own SES tenant. Sends are tagged with the team, so SES tracks each team’s bounces and complaints separately. If one team’s rates run high, SES pauses that team and nobody else.
  • SES’s reputation policy is on. A team whose bounce rate passes 15% or complaint rate passes 1% is paused automatically, and sends answer sending_paused until we’ve looked at it.
  • IPs are shared, domains are yours. Mail leaves on SES’s shared IP pools. We don’t offer dedicated IPs; below a few hundred thousand emails a month a dedicated IP usually hurts more than it helps, because it has no history of its own.

If you’d rather deliver through your own Resend, Postmark or SES account, you can keep Postboi’s log and webhooks and relay the delivery. Then that provider’s reputation is the one that counts, and the delivery record doesn’t include your mail.

Your domain’s authentication

Adding a domain gives you the records that make mail from it pass the checks Gmail and Yahoo require of bulk senders:

Record What it does
DKIM (3 CNAMEs) Signs every message with a key on your domain (SES Easy DKIM)
MAIL FROM bounce.<your domain>: an MX and an SPF TXT, so the return path is yours and SPF aligns
DMARC A starter p=none policy, offered only when your domain has none

With DKIM and the custom MAIL FROM in place, both SPF and DKIM align with your From address, so DMARC passes whichever one a receiver checks. Where your registrar supports Domain Connect, the records go in with one click. Until the MAIL FROM MX exists, SES falls back to its own return path, so you can send while DNS propagates.

Before you have a domain, mail goes from your address on send.postboi.email, our shared sending domain, with its authentication handled by us.

Keeping the shared reputation clean

Everyone on Postboi benefits from nobody on Postboi spamming. So:

  • New accounts warm up. For the first 7 days an account can send up to 1,000 emails a day, and until it verifies a domain, 100 a day, on every plan. Mailbox providers trust volume that grows steadily.
  • Hard bounces and complaints suppress the address. A permanent bounce, a spam complaint or an unsubscribe adds the address to your suppression list, and every later send to it is dropped before it reaches SES. Soft bounces (a full mailbox, a greylisting server) don’t suppress.
  • New accounts are watched. A complaint on a brand-new account, or a high hard-bounce rate from the shared domain, suspends the account until a person has looked. Sends from new accounts on the shared domain are also reviewed for phishing and impersonation, and addresses that imitate banks, tax offices or well-known brands can’t be claimed on it.
  • Blocklists are checked every night. At 03:00 UTC we ask the Spamhaus Domain Blocklist about the shared sending domain, every verified customer domain, its bounce. host, and the domains your recent mail links to. A new listing is a deliverability notification to your team the same morning, and another when it clears. We check domains rather than IPs: an SES IP listing is Amazon’s to clear and nothing you or we can act on.
  • List mail carries one-click unsubscribe. Sends to a list get List-Unsubscribe and List-Unsubscribe-Post headers (RFC 8058), which Gmail and Yahoo require of bulk senders, and the link suppresses the address in one request.

What you can do

  • Send from your own domain with its records in place. Shared-domain mail is fine to start with; your own domain builds a reputation that’s only yours.
  • Send only to people who asked. Double opt-in on lists keeps bounces and complaints near zero.
  • Keep transactional and bulk mail apart, for example mail.example.com for receipts and news.example.com for newsletters, so a newsletter complaint never slows a password reset.
  • Check an email before it goes. Email testing flags what gets mail clipped or filtered, and a hosted test gives you SPF, DKIM, DMARC and a spam score over the real message.
  • Watch the events. Bounces and complaints arrive as webhooks and in the message log, so a bad list shows up on day one rather than in a monthly report.