Mail is SO BUGGY it lags your computer and you have the updated colourful spinning wheel of death! But I've been able to connect my iCloud but not my Gmail emails.
How were you able to save it? I have the same problem. Aliases disappeared. When I try to edit them, no problem to enter the info but as soon as the Cancel/Save button screen appears the whole thing freezes. Does the exact same thing when I try to add them with commas in IMAP. As soon as Cancel/Save appears it's frozen and I have to force quit. Any ideas??
Is there a fix yet for this? I'm having the same issue too. I can't add my aliases back, nor send from them. I can, however, receive emails at those aliases. :/