[zaptheimpaler]

Are you talking about false negatives? The problem I have is with false positives. It regularly throws important legit email into spam.

Just the other day it threw an invoice from AWS into spam! Regularly throws financial docs into spam. Like it’s hard for me to imagine how that happens.

[sph]

Training a spam filter works both ways. Mark them as ‘not spam’ until it stops happening.

I never got a legit email end up in my Spam folder, so YMMV.

[brandonwindson]

Fastmail also uses global blocklists and reputation scores that can override your training. Could also be the sending IP is shared with bulk senders.

Marking as "not spam" should help over time. If it does not, create a rule to always deliver from that domain. That is the only way to guarantee it never happens again.