Open Radar

 
Summary:
When using Exchange, operations of move/copy/delete multiple messages are prone to fail.

These circumstances are PROBABLY related to an Exchange throttling condition.
https://msdn.microsoft.com/en-us/library/office/jj945066(v=exchg.150).aspx#bk_ThrottlingErrors

Steps to Reproduce:
1] With an Exchange account.
2] Select a "large" number of multiple messages.  Depending on the circumstance, "large" may be a dozen to hundreds.
3] Take an action that affects the location of all messages: Move to folder, copy to folder, or Delete.

Expected Results:
The operation should apply as expected.  If it was a copy, the messages should appear in the destination location. If it was a move, they should first disappear from the origin and then reappear at the destination.  If a delete, they should disappear from the origin and reappear in Trash/Deleted Items.

Actual Results:
At various times, for no apparent reason, these operations fail.  For a move or delete, most often the messages disappear from the source view, and then reappear.  An error dialog reports that "Mail was unable to move 24 messages to the "Trash" folder".  (or similar)

In some circumstances, the messages do NOT reappear. So far as the user can tell, they are lost to the ether.

Regression:
Has been observed in Mountain Lion through Mavericks and Yosemite, with both on-premises Exchange 2010, and Office 365 Exchange Online.