be sure to write your filters before receiving anything. Especially important if you're importing your email for the first time... and insanely annoying if you want to debug such an advanced filter.
as always with fastmail: It has great features... but always with a massive caveat.
Ooooof, wow, thanks for the heads up. There's no way that's going to work... I edit my filters and apply them retroactively... There's no way I can set them in stone the first time. :( is there any email service that doesn't have this limitation?
Its not on FastMail, its on Sieve. It is a hook that runs on receiving. To my knowledge if you want Sieve this is the only option. I use it with Protonmail and it is the same way. I also run it on my own mailserver.
One nice thing, for me at least, is it runs prior to the email ending up in your inbox and I am uses to Outlook rules were rules execute post arrival.
Sieve is an RFC email language. There's no reason Sieve recipes couldn't be applied to a corpus of existing email; that's an implementation detail of FastMail. Sure, it isn't necessarily the same as pre-receive (for example, anything you discarded the first time isn't going to show up again, and any manipulations made the first time aren't going to undo themselves). But it could be done; it's not really Sieve's problem.
