Sometimes Mail (mail.app) just seems to forget the passwords it needs. 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; perhaps there could be a network error instead, and if so you can adjust your Mail settings as much as you like and get no where. Tweaking settings that have previously worked in Mail just because they suddenly do not work could be a dumb move, if infact the problem turns out to be your service provider, because you may have just screwed up settings that should work.

But assuming other devices, such as an iPhone or another Mac or PC, can still send and receive using the same settings, the cause should lie with the Mac. Let’s look at the problem I am seeking to address here… 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 the one I have highlighted (which is for an old account I no longer use):

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.

I needed to run the command line in Windows XP as the administrator, something that I couldn’t just do by right clicking the Command Prompt in Accessories and selecting Run As Administrator, as you can in Vista or Windows 7. (I wanted to run the sfc.exe, and to do this it needed full administrator access). The quick way to do it, assuming you are logged in as a user with ordinary administrator or power user rights, is to go to the start menu, select Run…, type in CMD and press CTRL-SHIFT-ENTER on the keyboard. The command prompt shell will appear as normal, but you will find that you can issue commands that were previously restricted.

Sometimes emails from Windows users contain an attachment called winmail.dat or win.dat which mail applications on the mac do not automatically decode. If you reply asking the sender what is in the attachment they will most often say that they’d not attached anything. This is because their Microsoft email application mostly uses the dat file to store formatting code for the email to make it look nice to other users of the same software. However it is also sometimes a wrapper for attachments the sender does intend you to be able to open. Why Apple Mail does not automatically decode it I don’t know. The decoding software is open source.

So, in the interests of harmony with Windows users, here is a link to what you need to decode the dat files, TNEF’s Enough: For OS X 10.5 and above For OS X 10.4 Thanks to Josh Jacob