Fastmail’s built-in spam filter does a lot, but it can’t read your mind. This guide shows how a custom “Delete” rule gives you precise control over the junk you never want — and how to build it safely.
Two ways to fight junk
Leave Spam Protection on for the broad, ever-changing junk, and add a custom Delete rule for the specific repeat offenders it keeps missing. They complement each other. The trick is to target the root domain — in quotes.
Add a sender to your “Delete” rule
Reduce it to the root domain
Copy the junk sender’s full address, and reduce it to the root domain (drop the @ and everything before it).
Open Filters & Rules
Open Settings › Filters & Rules. Open your “Delete” rule, or click + Create rule and set the top dropdown to any.
Add the condition in quotes
Click Add condition, choose From, and paste the domain in quotes:
"baddomain.com".Set the action
Tick Delete to trash (Dr. Bob also ticks Mark read).
Name it and save
Name it Delete and click Save / Do it.
Never target a shared domain. Only quote domains that send nothing you want. Never add a root domain like "gmail.com" or "outlook.com" — that would trash mail from everyone using that provider.
Trash, not Spam. Sending junk to Trash (rather than Spam) keeps your Spam folder meaningful and lets you do one easy safety check before anything is gone for good.
New to rules? Start with Filters & Rules: The Basics.