Company email on a custom domain, built twice

Once as a mail server I administer, once as a serverless pipeline. Same result, opposite cost structures.

RoleSole engineer

ScopeDesign, build, run

Built inAbout six weeks

Still runningYes

A small business wanted addresses on its own domain without paying per seat for a suite it would barely open. Mail punishes carelessness quietly: authentication that is almost right sends invoices to spam, and storage that is almost right loses one of them. The requirement was never "send email" — it was email that is trusted, delivered, and recoverable.

Two builds

The server I run

A hosted stack I administer end to end, for a client who wants full control of storage and routing.

Postfix for transport, Dovecot for mailboxes

TLS everywhere, fail2ban at the edges

Nightly backups with a restore I have tested

Predictable cost, and my phone rings when it breaks

The serverless pipeline

Inbound and outbound mail through managed functions and an email API. Nothing to patch, nothing idling.

Functions handle receipt, parsing and routing

Objects in cheap storage instead of a mail spool

Near-zero cost at rest, scales on send

Less control, far less maintenance

The path a message takes

01Composethe app or client hands off a message

02AuthenticateSPF, DKIM signing, DMARC alignment

03Routeserver queue, or a function handler

04Deliverretries and bounce handling

05Storemailbox or object storage, backed up

What went wrong first

Early sends passed every test I had written and still landed in spam. The fix was not code, it was DNS discipline: SPF, DKIM, and a DMARC policy that starts at none, gets read for a fortnight, then tightens. Deliverability is now a number I watch rather than a box I ticked, and the reverse-DNS and warm-up notes live in the runbook so nobody rediscovers them at midnight.

Where it landed

Staff addresses live on the company domain, with no per-seat suite licence.

Deliverability is monitored rather than assumed — DMARC reports get read.

A written runbook, so recovery does not depend on me being reachable.