The one-sentence version#
Transactional email is triggered by a user action (receipts, password resets, alerts) and is exempt from most marketing consent rules. Marketing email promotes products and requires consent and unsubscribe links.
Why you should care#
Mixing the two on one domain or stream means a bad campaign can block password resets. Separating them protects critical mail.
The mental model#
Think of transactional email as a contract between you and the mailbox providers receiving your mail. You publish or configure something they can check; they check it on every message; the result feeds their decision about where your message lands. Everything below is about making that check pass consistently.
Your first setup, step by step#
- Send transactional mail from a dedicated subdomain (for example mail.yourdomain.com) or separate stream.
- Send marketing from a different subdomain (news.yourdomain.com).
- Keep promotional content out of transactional messages to preserve their exemption.
- Apply DMARC to the organizational domain so both subdomains are covered.
Words you will see#
- Mailbox provider: Gmail, Microsoft, Yahoo, Apple, and the corporate gateways that decide where mail lands.
- Authentication: proof that a message is from who it says it is (SPF, DKIM, DMARC).
- Reputation: the provider's running score of your domain and IP.
- Placement: whether a message reaches the inbox, spam, or is rejected.
Common mistakes#
- Adding upsell banners to receipts, which reclassifies them as marketing under many laws.
- Using one shared IP pool for both streams.
Frequently asked questions#
Do transactional emails need an unsubscribe link?
Not under CAN-SPAM if purely transactional. Gmail's bulk-sender rules still expect one-click unsubscribe for anything sent at volume, so many senders include it anyway.