2 Possible Fixes for Mail SMTP Sending Errors in Mac OS X

Some Mac users who updated MacOS have found Mail app to experience errors or problems when trying to send email. Typically this is in the form of an SMTP server connection error, a mailbox that’s seemingly stuck offline, a repeated request for a password from Mail app (a fairly common issue which we’ve fixed before), or some other connection error. If you’re experiencing any of these issues with Mail app, the solution is likely simple as we’ll show you.

A quick note for Gmail users experiencing an inbound or outbound mail problem, a connection failure, or an error message that says that Mail “Cannot send message using the server smtp.gmail.com.” or “The Gmail SMTP connection to server smtp.gmail.com failed.” While either of the solutions outlined here are likely to resolve the problem, it’s also possible that you are experiencing the error if you’re using 2-Factor Authentication on the Google account. If you are using 2-factor authentication, you need to generate an app-specific password from Google here and use that in troubleshooting solution #1 rather than your normal account password. Keep that in mind as you work through this process.

1: Fix Sending Mail Errors in Mac OS X with Credentials

If you’re getting cannot send mail errors only when trying to send mail or connect to your emails SMTP server, the solution is probably the same as when Mail repeatedly asks for a password, you simply need to re-authenticate and provide the SMTP server your login and password as set in the mail preferences:

1. Open Mail app and go to the Mail menu, then select “Preferences”
2. Choose the “Accounts” tab in the preferences window
3. Select the mail account that is experiencing problems and/or errors
4. Look under the ‘Account Information’ tab and click on “Outgoing Mail Server (SMTP)” and choose “Edit SMTP Server List”
5. Select the ‘Advanced’ tab at the Edit SMTP Server List screen
6. Re-enter your login and password credentials for the affected email account here



7. Now click “OK” and close Preferences, selecting to “Save” when asked about changes
8. Compose a new email message and send it (to yourself, us, your Mom, Santa, whoever, this is just a test email)

The email should now send as usual.

Once that email goes through, you may have some unsent messages sitting in your outbox, they will send automatically in time, but you can also synchronize the mail account to push it along.

If you’re still experiencing Mail problems with stuck outbound messages and SMTP server errors, move to the next trick.

2: Fix Outbound Email SMTP Failures in Mail App Manually on Mac

The above trick should do the job and resolve your issues, but if you have confirmed the login and password are set and accurate and still find yourself still struggling with Mail app failing to send emails and your outbox filling up with unsent email, another possible solution was found by an Apple support forums user. Note that this is modifying the email account to allow for insecure authentication, which is potentially a security risk, making this an unacceptable solution for some users. If this is due to a bug in OS X Yosemite Mail app, a fix will likely be released to address the issue without having to modify any plist file yourself. This is a bit more advanced and you’ll probably want to backup your Mac (or at least the Accounts.plist file) before modifying anything here:

1. Quit out of the Mail app
2. From the Mac OS X Finder, hit Command+Shift+G and enter the following path:

~/Library/Mail/V2/MailData/

3. Make a copy of the “Accounts.plist” file to your desktop – this will serve as a backup in case you break something, just swap that file back



4. Open the file named “Accounts.plist” into your text editor of choice
5. Locate the following line:

<key>UserAllowsInsecureAuthentication</key>
<false/>


6. Replace the “false” text with “true” so that it reads <true/> then save the Accounts.plist file



7. Close TextWrangler or TextEdit and then relaunch Mail app
8. Try to send an email as usual, it should work as usual

As already mentioned, this is placing a modification that allows for potentially insecure authentication for that email account, making it impractical for users who live exclusively on public wifi networks or high security risk environments.

If you have multiple accounts configured in Mail app that are having problems, you would need to locate the account you’re having trouble with in the Accounts.plist file. Of course if the problem is happening with all of the accounts, then you’d want to make that change for all of the accounts that are effected with failing SMTP responses.

Did #1 or #2 resolve your Mail app problems with MacOS or Mac OS X? Can you send and receive email as usual again? Let us know in the comments.