Transactional mail is a receipt, a password reset, an order confirmation: expected, one at a time, and it must arrive. A newsletter goes to thousands of people at once, some of whom will mark it as spam. Sending both from the same domain means the second damages the first.

Why it matters

Reputation is tracked per sending domain and per IP. Enough complaints about a campaign and the whole domain is treated with suspicion - including the password reset somebody is waiting for right now, which is the one message that must never be delayed.

Separate the domains

receipts and resets   ->  mail.yourdomain.com\nnewsletters           ->  news.yourdomain.com

Each subdomain gets its own SPF and DKIM records and builds its own reputation. A bad campaign week affects the newsletter subdomain and nothing else.

They also need different handling

  • Transactional - send immediately, retry hard on failure, alert somebody when it fails, and never add marketing to it.
  • Newsletters - send in batches, honour unsubscribes instantly, and stop sending to addresses that bounce.
Do not put a promotion in a receipt to avoid the unsubscribe rules. In most jurisdictions that makes the receipt a marketing message, and it needs the same consent and the same unsubscribe link.

List-Unsubscribe, on the newsletter

List-Unsubscribe: <https://news.yourdomain.com/u/abc123>, <mailto:unsub@news.yourdomain.com>\nList-Unsubscribe-Post: List-Unsubscribe=One-Click

Large providers now require this for bulk mail. Without it the unsubscribe button in the mail client becomes the spam button instead, which is far more expensive to your reputation.

Watch them separately

Bounce rate and complaint rate per domain. Transactional bounces mean an address problem; newsletter complaints mean a content or consent problem. Mixed together, neither number means anything.

If a new domain is involved, start slowly - see warming a new sending domain.