One thing I've noticed with apple mail and Gmail is that Gmail won't send out anything that it regards as spam or any e-mails that you send to yourself. Just some info

apple mail unpredictable in general
 

i've found "get all new mail" doesn't. i have all multiple accounts and want them all to check every 5 minutes. however, the program is pretty random about what it wants to download. opening the activity viewer when i do a manual check confirms this (only 1 of 3 accounts is actually checked). I have to select "get new mail" and highlight each account individually. suddenly I'm downloading 100's of emails.