I’m having more issues with important e-mail getting caught in our corporate spam filter. In almost all cases they are messages from vendors that contain a signature block with a marketing message of some sort. I think these types of messages are doomed from now on. Imperfect spam filtering is a fact of life for the time being. Due to that, people will have to learn how to craft their messages in a way that does not trigger them if they want to communicate via e-mail. A good start is to pull those marketing messages from your signature.