Email intermittently says it can't connect to the server but connection doctor says I'm connected

Question

I have both my Yahoo and work email accounts on  my MacBook Pro. Intermittently, my work email refuses to send, giving me the error message that it can't connect to the server. Connection doctor says work email is connected to the internet, and some emails will go while others won't. Have checked server settings agains my Iphone, and they are identical. No problem emailing from the phone. Help?

Answer 1

Please follow these directions to delete the Mail "sandbox" folder.
Back up all data.
Triple-click the line below 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.
Quit and relaunch 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. 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. Post your results.
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 (command-C). In the Finder, select
Go ▹ Go to Folder...
from the menu bar, paste into the box that opens (command-V). You won't see what you pasted because a line break is included. Press return.