Apple Support Discussions poster "NewYorkYogi" reports:
Sometimes, no matter what, Mail wants me to reenter the password on my email account. When this happens, quitting Mail, unlocking the keychain, and re-invoking Mail sometimes fixes the problem. When it does not, I have to re-enter the email password. Check Save to Keychain doesn't seem to help much. After I have re-entered the email password, Mail appears to work.
Mail requires access to your Keychain so that it can obtain passwords to access messages on your mail server. If you lock Keychain, Mail will have to ask permission each time it attempts to retrieve or send mail. The issue here is that even when Keychain is unlocked, Mail is requesting that users enter their password. ASD user "Lawrence Cragg" adds an opinion:
I never experienced this problem with Leopard but it's absolutely chronic with Snow Leopard on an iMac. I cannot associate this problem with any connection difficulty although that would be difficult to do. No matter, the net effect is infuriating: I have to go into Mail's preferences to retype the password.
A Possible Solution:
My personal experience with this issue has lead me to this solution, which has two variables. If you have recently changed the password on your mail account, you may have a conflicting entry in Keychain causing Mail to be confused. Open Keychain Access (Applications > Utilities) and search your passwords. If you have more than one password for your current mail account, delete any old ones. To take effect, you may have to log out, then back in. The variable on this is, if you only have one password for your current mail account, simply delete that password entry. The next time you open Mail, you will be asked for your password - enter it correctly and be sure to check to save the password to your Keychain.
Users will want to be sure that all their information is correctly entered in their Mail accounts. If you have recently upgraded to Snow Leopard or restored from a backup, you should delete the account from Mail completely and re-enter it. Other attempts at solutions have lead users to rebuild their mailboxes (Mail menu bar > Mailbox > Rebuild) or to run Keychain Access' keychain first aid. Most report that these solutions offer temporary fixes, but the problem returns.
As always, we will continue to watch this problem as it develops and update you when we find more solutions. Experiencing issues, have questions, want to let us know about an issue we should report on? Email Us!