A password reset and a newsletter are both email. Treating them as the same kind of email is one of the more expensive mistakes a small team can make.
The distinction
Transactional email is triggered by something the recipient did: an order, a reset request, a booking. The recipient is expecting it. Complaint rates are near zero.
Marketing email is sent because you decided to send it. The recipient consented at some point, possibly a while ago. Complaint rates are meaningfully above zero, and that is normal.
The legal treatment differs — most jurisdictions do not require an unsubscribe link on genuinely transactional mail — but the operational reason to separate them is simpler than compliance.
Why the separation is technical, not just tidy
Mailbox providers score your sending domain on recipient behaviour. Marketing mail generates complaints and ignored messages; that is the cost of doing it. Transactional mail generates opens and clicks because people are waiting for it.
Send both from the same domain and the marketing complaints drag down the reputation that your password resets depend on. The failure is asymmetric and brutal: nobody notices slightly worse newsletter delivery, but everybody notices when password resets stop arriving.
The fix
Use a subdomain per stream. mail.example.com for marketing, notify.example.com for transactional. Reputation is tracked per subdomain, so a bad marketing month does not touch your resets.
Do not put marketing content in transactional mail. A promotional banner in an order confirmation reclassifies that message. It is also the exact thing that makes people mark receipts as spam.
Keep suppression lists separate but linked. Unsubscribing from marketing must not stop a password reset. Being on a hard-bounce list must stop both.
The grey area nobody agrees on
Shipping notifications with a “you might also like” block. A receipt that mentions a referral programme. A booking confirmation carrying a survey link.
There is no clean answer, and regulators differ. A workable rule: if removing the promotional part would still leave a message you were obliged to send, it is transactional with an add-on. If removing it leaves nothing, it was marketing wearing a receipt’s clothes.