Although I can’t promise this solution will work in every case, I can say that it worked with my last three encounters with this bug. One day your mail is collected OK by the Mac’s Mail application, and then suddenly it starts asking for your password to send or receive. Of course, Mail might not be at fault; there could be a network error, and if so you can tweak your settings as much as you like and get no where. Tweaking settings that have previously worked in Mail that suddenly do not is dumb if infact the problem turns out to be your service provider. But assuming other devices, such as an iPhone, can send and receive using the same settings, the cause should lie with the Mac.

Specifically, Mail asks for the password and even though you makes sure the remember checkbox is checked it ignores this and asks again and probably gets no mail.

This error is longstanding with Mail.app. I have fixed it on a new iMac running Snow Leopard, for instance, and also on machines as old as a G3 iBook running Tiger.

So if this sounds familiar try the following fix:

Locate and open Keychain Access in the Utilities folder, in the Applications folder. Look for the pop, mail or smtp settings that Mail is complaining aren’t working. They will probably look like this:

a mail keychain

Double-click to edit. Check the Show Password to look see if it is the one you expect. Then click the Access Control bar to get:

Keychain Access Control

Now grant access to this password to other applications besides Mail.app. Click the radio button “Allow all applications to access this item”.

Save and close. Do this with any other email account Mail complains about, covering settings for both incoming and outgoing mail. After this I find Mail asks one more time but that this time the password sticks.