Outgoing mail gets stuck in outbox?

The solution below was found at: https://discussions.apple.com/thread/6351214

It appears to have solved the issue for me.

Linc Davis

Jun 9, 2014 9:53 PM

Re: Mail is getting stuck in my outbox?

in response to Hydro99

Please follow these directions to delete the Mail "sandbox" folders. In OS X 10.9 there are two sandboxes, while in 10.8 there is only one. If you're running a version older than 10.8, this comment isn't applicable.

Back up all data.

Triple-click anywhere in the line below on this page to select it:

~/Library/Containers/com.apple.mail

Right-click or control-click the highlighted line and select

Services ▹ Reveal

from the contextual menu.* A Finder window should open with a folder named "com.apple.mail" selected. If it does, move the selected folder—not just its contents—to the Desktop. Leave the Finder window open for now.

Log out and log back in. Launch Mail and test. If the problem is resolved, you may have to recreate some of your Mail settings. You can then delete the folder you moved and close the Finder window.

This action will delete any custom Mail stationery that you have created. If you want to preserve it, ask for instructions.

If you still have the problem, quit Mail again and put the folder back where it was, overwriting the one that may have been created in its place. Repeat with this line:

~/Library/Containers/com.apple.MailServiceAgent

Caution: If you change any of the contents of the sandbox, but leave the folder itself in place, Mail may crash or not launch at all. Deleting the whole sandbox will cause it to be rebuilt automatically.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select

Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.

If mail is box is corrupted we take back up of all mails & delete corrupted IMAP account .

once again fresh IMAP account is created , you can transfer all mails .

some apple articles are there it might help you : Mail (Yosemite): Verify an account’s outgoing mail server

Use Mail on your Mac - Apple Support

This exact same problem has been plaguing my mac for the last two days. It seems that the gmail messages will send eventually (possibly after hours of waiting), but any message trying to send through a Microsoft Exchange Server sits permanently in the "On My Mac" Outbox, and cannot be moved to the drafts folder or any other folder.

This problem is not solved by reopening the app, rebooting the system, disabling and re-enabling the exchange server account between app restarts.

Looking for an elegant solution to this issue which has serious implications for my ability to use my Mac.

MacBook Pro Haswell Late 2013

Yosemite 10.10.1

Didn't solve the problem for me, or rather: the message is sent relatvely fast, but the message appears to be sent through an "on my Mac" Outbox, rather than the Exchange Outbox from which it should leave. I have never seen before an "on my Mac" Outbox! I am running 10.11.3 on a MacBook Pro Retina mid-2015. Is this another of the Mail bugs of El Capitan???

I'm having this issue now, only started a couple of days ago. I'm using Mac Mail, compose and send an email and it looks like it sends, the blue progress bar appears and goes. Look at my mail again and the email is still in my outbox. Tried restarting the app and the mac, even tried theidentities solution, but that didn't work. Even tried calling BT who deal with our outgoing mail and they said they can't see any issues. Trouble is, when we called BT it seemed to have started working again. But this is the thing, one minute it will work as normal and the next minute messages will get stuck in my outbox again, very frustrating. This is at my work and everyone in the studio is suffering the same issue. If anyone has any cure or suggestion to this issue, then please share, it wil be much appreciated.