Mail.app: Cannot send mail, fixes

[Updated March 1st, 2007]

Apple's Mail.app can suddenly and inexplicably fail to send e-mail through SMTP (outgoing) servers. A few relatively simple fixes for this issue are as follows:

Delete outbox folder In some cases, the Mail.app outbox folder -- or messages contained therein -- can become inexplicably corrupt. In order to rectify this issue, use these steps:

1. Quit Mail.app
2. Navigate to ~/Library/Mail/Mailboxes/ (~ represents the current user's home directory, e.g. /Users/username)
3. Move the folder named Outbox.mbox to a separate location.
4. Relaunch Mail.app
5. Try sending mail again

Delete Mail caches Mail.app caches can become corrupt, interfering with proper mail sending routines. In order to delete these potentially problematic caches, use these steps:

1. Quit Mail.app
2. Navigate to ~/Library/Caches
3. Delete the folder Mail
4. Relaunch Mail.app
5. Try sending mail again

Switch ports In some cases outgoing mail issues can be solved by switching the SMTP port through which you access your ISP's sendmail server.

In order to change this setting, use the following process:

1. Launch Mail.app
2. Under the "Mail" menu, select "Preferences"
3. Click "Server Settings" under to the "Outgoing Mail Server (SMTP)" heading
4. Set the SMTP port to the one specified by your ISP (for users of Comcast [and some other ISPs], try port 25)
5. Back in the Mail.app preference window, click the "Advanced" tab
6. Set the appropriate port number (for users of Comcast [and some other ISPs] try 110)

Note that you may also need to turn off SSL (secure socket layer) in both of these areas (for the SMTP server and the incoming server).

Re-establish accounts In the case of some sending problems with IMAP accounts, the only effective solution is to delete then re-establish the afflicted account via these steps:

1. In Mail.app, go to Preferences under the File menu
2. Click on the "Accounts" button
3. Select the problematic account(s) then click the minus (-) button to delete it
4. Quit Mail.app
5. Navigate to ~/Library/Preferences and delete the file com.apple.mail.plist
6. Relaunch Mail.app
7. Re-establish account information using the automatic setup tool, or from the "Accounts" pane of Preferences by clicking the plus ( ) button

Check SMTP server Contact your ISP or e-mail service and ask for the current, correct SMTP server. In some cases, old SMTP servers become deprecated, or no longer function properly.

MacFixIt reader Nathalie provides a case example:

"For several days I was unable to send email from earthlink account. I had been sending email using smtpauth.earthlink.net but after changing all sorts of things, such as port etc., I changed to smtp.earthlink.net and that worked."

Check recipient list Unknown recipients can cause mail sending to fail. Make sure that there are no spelling errors, and that all e-mail addresses being sent to are existent.

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