How to recover lost Mail content after Yosemite update? I have just updated Yosemite on my MacBook Air and the outgoing mails cannot be sent - the SMTP-connection fails.
It worked OK a few seconds before the upgrade was started.
I wanted the Outgoing mails to work again. 

I did the following in Mail Version 8.2 (2104)  


Opened  ~/Library/Mail/V2/MailData/Accounts.plist  
Found the block of data that contains the offending mail account  
Found the line within this block that says UserAllowsInsecureAuthentication  
Changed the line below this from &lt;false/&gt; to &lt;true/&gt;  
Quit TextEdit  
Launched Mail 


Now I don’t see my mail account and the content.
In mail 8.2 os x yosemite 10.10.5 preferences, rebuild accounts take offline accounts take on line and other tools are grey. 

Can you tell me how to fix it in to see the email accounts and the contents of all my emails in box, send, trash, junk, archives etc.
Quit Mail
Find &amp; trash the 3 files in ~/Library/Mail/V2/MailData/ that begin with Envelope Index...
Launch Mail.

That should rebuild the database.

It may not fix your connection issue, but ought to return the missing data.  

To fix the connection, try unchecking 'Automatically detect &amp; maintain..." in Prefs > Accounts > SMTP Settings/Edit