Mail stream
A category of mail sent with its own identity (IP, DKIM domain or subdomain, From address), such as marketing kept apart from transactional mail, so each builds its own reputation.
What it means
Providers ask senders to separate types of mail. Google advises a different IP address for each message type if you send from several (account notifications on one, promotions on another) and a consistent From address per category. Yahoo says not to send bulk or marketing mail from the IPs used for user mail, transactional mail or alerts, because each IP and DKIM domain has its own reputation. Apple asks bulk senders to keep IPs and domains consistent while segmenting marketing and transactional streams.
M3AAWG recommends subdomains named for their purpose, such as offers.example.com for marketing and info.example.com for transactional mail.
The benefit is containment: a campaign that draws complaints does not drag password resets and receipts into the spam folder.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- Google: Email sender guidelinessupport.google.com
- Yahoo Sender Hub: Sender requirements and recommendationssenders.yahooinc.com
- Apple Support: Postmaster information for iCloud Mailsupport.apple.com
- M3AAWG Sender Best Common Practices, version 4.0 (August 2026)m3aawg.org
- Amazon SES: Creating dedicated IP poolsdocs.aws.amazon.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes