Why does Apple Mail hang in OS X 10.10 Yosemite?
Answer: Apple added several new features to the default Mail client (Mail.app) in Yosemite (OS X 10.10). Some of the features, such as Mail Drop and Markup, are welcome additions. Other updates seem to have caused more harm than good.
One example is a new feature hidden in the Advanced settings of each mail account called:
"Automatically detect and maintain account settings"
This option is checked by default for all of your mail accounts. Nobody knows exactly what this setting is for or what it does, but having it active can cause Mail.app to stall and hang, making it unresponsive.
If you have had problems with Apple mail hanging, follow these steps to fix the issue:
This process worked for me. Hopefully it works for you too.
Entered: September 12, 2015 – by Per Christensson