I'm importing mail from our own mail server via POP3 (without removing mail on import). It worked flawlessly for a few years, but recently gmail reimported all old mail again and showed up us unread (edit: all the mail from a certain date in mid-2012, not all the mail since the beginning of time). I thought it was some kind of our server misconfiguration, blamed our sysadmin and sent all the old mail to trash in gmail. The problem, however, repeated, and our admin claims that no changes were made to our server configuration. What to do to prevent old mail showing up again in inbox? Gmail import settings are as follows:
Import mail using POP3
username: [my mail at company domain]
password: [my password]
pop server: [our pop server address], port: 110
[YES]: Leave a copy of received message on the server
[NO]: Always use SSL connection (that probably should get switched on, but it's a different story)
[NO]: Apply a label
[NO]: Archive incoming mail