Mail errantly classifying mail as junk

[Marc Anthony]

Apple Mail keeps moving one particular sender (who is in my address book) to the junk folder. It's so irritating, that I completely turned off junk mail filtering, but it's still doing it. I'm not sure how. OS 10.9.5, if it makes a difference. Do I just need to throw away my Mail preferences?

[Onamuji]

Have you tried marking that person's emails as "not junk" and moving the messages to another folder?

[Marc Anthony]

Yes. I tried that first on a couple different occasions, thinking that might "train" the filter. It didn't.

[Onamuji]

Mail follows spam-headers from mail servers.

Possible that your server is marking it as probably junk?