Rules in Mail randomly don't apply I have a very simple rule set up in Mail like the following:

If [any] of the following conditions are met:

[From] [Contains] @gmail.com

Perform the following actions:

[Move Message] to mailbox: Gmail


That's about as basic as you can get: if an email comes from a certain domain, move it to a certain folder. That's it.

But it doesn't always work! Seemingly random messages will just sit in my inbox and never move to the folder unless I manually select them and Apply Rules.

Am I misunderstanding how rules are supposed to work? What's going on?
Try deleting the rule and creating a new one. Mail seems to randomly corrupt things on even the most well-maintained machines, the past few OS iterations. Passwords disappear. Then there is the step of trashing your Mail preferences, as preference files do get corrupt.