My spam filter is too strict

A filter letting too much spam through is annoying. A filter blocking real email costs money. The second problem is the worse one and the less visible.

Look at why first

A blocked message almost always carries a reason: score too high, sender on a blocklist, or failed domain authentication. That reason determines the fix.

If the sender is at fault

Many blocks are correct: the sender has no valid SPF or DKIM. The right fix is to tell the sender, not to weaken your filter.

Exceptions

Whitelist specific addresses, not entire domains. Allowing a whole domain is the fastest route to real spam.

Check regularly

Go through the spam folder once a week. It is the only way to know what you are missing — a filter does not tell you what it blocked.

Do not switch it off

A disabled filter solves the symptom and leaves you the real problem. Tune the threshold rather than opening everything up.