
Not all users encounter this issue with Mail app after installing an OS X update, and though the reason is unclear, it’s possible the problematic setups had configured an email account some time ago, and could be using legacy settings for a specific mail server. SMTP mail accounts, these solutions should do the trick. That should resolve whatever Mail problems have occurred in OS X after installing OS X 10.10.4 or OS X 10.11 El Capitan, but if you continue to encounter trouble, specifically with If you’ve completed this and OS X Mail app still hangs on launch but does not offer any obvious errors, your next troubleshooting step should be to rebuild the Mailbox as described here, which should resolve that issue. Yes relaunching and re-checking a box is a little frustrating and can be a little tedious, but it does seem to work to resolve any problems with Mail app, as the automatic detection of mail account settings will adjust server settings to accommodate the Mail app configuration. Repeat this process for other email accounts in Mail app if necessary.If it is checked, uncheck it, then quit and relaunch Mail app, then go back to the same preference setting and check the box again, then relaunch Mail app yet again.

If it is unchecked, check it – then relaunch Mail app.

