The scenario is this:

1 Exchange 2013 mailbox server currently hosting all user mailboxes

2 Exchange 2013 mailbox servers, brand new.  Users will be moved here eventually.

The 2 new mailbox servers will be part of a dag.  Today I created 2 MB databases on server 1.  Created the DAG. Created 2 networks, 1 for replication, the other for mapi. Enabled DAC mode.  Again there are no production mailboxes on these 2 new databases.  Everything looked fine.  When attempting to make database copies to the other node I get the error:

Error: An error occurred while performing the seed operation. Error: Failed to open a log truncation context to  source server Hresult: 0xc7ff1004. Error: Error returned from an ESE function call (-1305).

which I have seen the posts about this error and how to fix.  But somewhere during the creation of the DAG, configuration of the DAG, and attempt to make a database copy, all email flow ceased.  No internal\external mail could be sent or received.  No NDR's, no indication of what was going on.  I immediately disabled DAC, deleted the database copy that had failed when trying to create the copy, removed the mailbox servers from the DAG, and mail started flowing again.  Again, no production users were on either one of these servers.  I did not delete the DAG, in fact I added the 2 servers back, but did not attempt any database copy operations.  Mail is still flowing fine.  Any ideas on what would cause mail to quite flowing during this operation would greatly be appreciated.

Hi,

According to your description, I recommend you should use the trace logs to find out where the emails when the mailflow ceased.

Additional, did you fix the error ?

If yes, I suggest you attempt to make database copy again, and check the result.

If the issue remains, please gather the app logs and mail trace logs, and post it.

Thanks.