Transactional vs marketing email: why the split matters
They look the same in code and behave completely differently in the inbox. Separating them protects the mail your product cannot function without.
Both are "an email your app sends". That is where the similarity ends.
The distinction that matters
Transactional mail is a response to something a specific person did: a password reset, a receipt, a shipping notice, a verification code. It is expected, usually urgent, and opened at rates above 60%.
Marketing mail is sent because you decided to send it: a newsletter, an announcement, a promotion. It goes to many people at once, is opened at 15–25%, and someone will always mark it as spam.
That last point is the whole argument. Marketing mail attracts complaints as a matter of course. Transactional mail must not be anywhere near them.
Why sharing a domain is a bad trade
Reputation is tracked per sending domain. Send both streams from yourdomain.com and a campaign that collects complaints will push your password resets toward spam.
The failure is quiet and badly timed. Nothing errors. Your logs show successful delivery. Support tickets start arriving about codes that "never came", usually a day or two after a campaign, so the connection is rarely obvious.
The setup
Use separate subdomains:
notify.yourdomain.com— transactional onlymail.yourdomain.com— campaigns and newsletters
Authenticate both. Warm both. Keep them apart permanently. Your root domain stays clean for person-to-person mail.
Rules that differ
Consent. Marketing mail needs it. Transactional mail does not, because the recipient triggered it.
Unsubscribe. Marketing mail legally requires a working unsubscribe. Transactional mail should not carry one — you cannot let someone opt out of password resets. Provide notification preferences instead.
Timing. Transactional mail sends immediately; a verification code arriving ten minutes late is a failed signup. Campaigns can queue and pace themselves.
Retries. A failed receipt is worth retrying. A failed newsletter is not worth the reputation cost.
Where teams get caught
The grey area is real. A receipt with a promotional footer is a hybrid, and regulators tend to judge by the primary purpose. If the main reason for sending is commercial, treat it as marketing — consent, unsubscribe, the separate subdomain, all of it.
The safer instinct: if you would be uncomfortable defending it as "they asked for this", it is marketing.