What is Suppression List?
A persistent do-not-send registry of bounced addresses, spam complainants, and unsubscribes consulted before every send. BYOB’s email broker checks suppression first, so one bad address never poisons a whole campaign.
Example
Before a campaign launch, the email broker screens recipients against suppression: prior bounces, complaints, and unsubscribes drop out silently. The send reaches fewer addresses but every one of them is legally and technically mailable.
What people get wrong
Deleting suppressions to inflate list size before a big send. Re-mailing complainants invites blocks that punish future transactional mail too.
Frequently asked questions
Can suppressed addresses ever return?
Yes, through a fresh, explicit opt-in that clears the old complaint or bounce state. Never restore addresses in bulk or on assumption.
Related terms
Bounce Handling
Processing delivery failures by classifying hard bounces (dead addresses) separately from soft ones (full inbox, throttling). The project inbox worker records outcomes so dead addresses stop receiving retries automatically.
Complaint Feedback Loop
A mailbox-provider channel reporting when recipients mark mail as spam, so senders can suppress complainers immediately. Ignoring complaints burns sender reputation far faster than any single campaign gains.
Transactional vs Marketing Email
Account messages users expect (receipts, resets, alerts) versus promotional campaigns needing consent and easy opt-out. Separating the streams protects critical delivery when marketing complaints spike.
Project Inbox Worker
A mail-receiving Worker that turns inbound email into database rows. Apps get email-triggered workflows without running a mail server.
Return-Path Alignment
Matching the envelope sender domain used for SPF with the visible From domain that recipients see. Aligned domains let inbox providers credit authentication to the brand instead of the sending platform.
Sender Identity
The verified domain or address a provider is permitted to send from, proven through DNS records. BYOB projects verify sending domains before campaigns so transactional mail leaves from a trusted name.