This article from Media Temple covers a number of issues you might experience with Apple Mail, and information on how to fix them.
Article Contents:
Overview FAQs
Not receiving email
Not Sending or Receiving email
Not able to send email
Sent messages not saved
Overview
Apple Mail is the default email client that comes with every Mac using OS X 10.0 or later. This guide provides information on the most common issues for Apple Mail.
This is for the latest version of Apple Mail, version 5.0 on Lion OS 10.7. Your version of Apple Mail may vary.
Not sure which OS X version you're running? Check out: How do I find my operating system (OS) version on a Mac?
FAQs
Q: What's the best way to assure my emails in Mail are backed up?
A: Mac OS X comes with a feature called Time Machine which will maintain backups of your entire machine including emails in Mail when configured properly. However it is also good practice to perform manual backups, you can find detailed instructions about exporting a copy of your mailbox at http://support.apple.com/kb/PH4811.
Q: Mail will repeatedly ask for my password, how do I stop it?
A: There are several issues that may cause this problem to arise. Most often, verifying your settings will resolve this issue. If this fails to resolve the issue, then you will need to reset the password for your email address within the (mt) AccountCenter, and provide Mail the new password.
Q: Mail states it can't "Verify Certificate". What does this mean?
A: This occurs because you are set to use a secure SSL connection, which is a very good thing. However, in order to use a SSL connection with the Grid you must set the Incoming and Outgoing Mail Server to be your access domain. Otherwise, you can opt to continue or ignore the warning, although you may continue to receive this message in the future.
Q: Emails sent in Mail do not appear in my Sent Folder, why?
A: When using IMAP, as we recommend for the Grid, Mail requires you provide a specific folder to save sent messages. Follow these simple steps to configure this:
- Click and highlight the "Sent" folder for your account.
- Click the "Mailbox" menu
- Choose "Use This Mailbox For"
- Choose "Sent"
Not receiving email
Once in a while, your Mail.app (sometimes referred to as "Apple Mail" or "Mac Mail"), stops receiving new mail. You may be able to verify that you are getting new mail via webmail, another email client or computer, or even via a mobile phone. When this happens, the fix is extraordinarily easy!
Here's how: From inside the Mail.app, click the Mailbox menu (see Figure 1):
- Choose "take all accounts offline", and wait 10 seconds.
- Choose "take all accounts online".

Figure 1: Follow these steps to refresh your Mail application.
You should begin seeing your new mail flow into your inbox.
Not Sending or Receiving email
If your mailbox is constantly spinning and mail is not coming or going, it means IMAP is not syncing. In this case, try these steps:
- Close mail.app.
- Go to /Users/your_profile/Library/Mail/IMAP-account_concerned/.
- Delete hidden folder .OfflineCache.
- Start mail.app again.
Note: This will not delete any messages.
Not able to send email
First, close Mail.app completely. You can do this by either command-Q or click on Mail and selecting Quit. Then re-open the application by clicking on the stamp icon in your dock.
Next, confirm that your email settings are configured correctly. For more information, please read this article: Email setup for Apple Mail.
Once you've confirmed that your account settings are correct, let's check your outgoing settings.
Sent messages not saved
Yes, this can occur when using IMAP. Please read this article for more information: Email set up for Apple Mail.
Nested inboxes
Figure 2: The dreaded nested inboxes.
In IMAP accounts, users have the option to specify their root folder for Mail accounts (also known as the "IMAP Path Prefix"), which isolates folders the mail program uses from others in the user's account on the email server. When users have experimented with the prefix entry, some were able to fix the problem even though this has not been the case for others.
Potential Fixes
Change the IMAP Path Prefix. Go to Mail's preferences and in the "Accounts" section select the problematic account. Then go to the "Advanced" tab and change the field to the value given by the account provider. If the problem persists, users might try changing the case of the path prefix entry. For instance, with Google's Gmail, the default is to use "[Gmail]" as the prefix, but users might try "[GMAIL]" or "[gmail]" as well. In addition, since the prefix is actually a folder path, users might try putting a forward slash "/" at the end of the prefix, which may help indicate that the path ends in a folder. Some users might also have success with adding the "INBOX" name at the end of the IMAP prefix, but it is recommended that users try both with and without this.
Change Mailbox Behavior
In Figure 2, the Trash mailbox is at the end of the tree of nested inboxes. This could indicate the problem lies in how the Trash folder is being dealt with. As such, users might try toggling combinations of the options to "Move deleted messages to the Trash mailbox", and "Store deleted messages on the server", which are available in the "Mailbox Behaviors" tab in the "Accounts" preferences.
Reset Mail's preferences
The IMAP prefix settings are stored in the account settings in the preferences files for Mail, and if there is a corruption in the preference files that is preventing settings changes from working correctly, then this could be why the problems reoccur for some users. The Mail preferences file is called "com.apple.Mail.plist" and is located in the /username/Library/Preferences/ folder. Removing this file will require users to re-enter account information, but Mailbox setup and downloaded messages will all remain intact.