This question is about Exchange 2010 and not 2013.

Most online resources says the only reason to suspend a mailbox database copy if it's to be taken down for maintenance. However we're constantly getting Internet line issues between our 2 sites such that the copy queue length goes up to > 10,000 daily and on a bad day, sometimes this queue length is preventing incoming mails from external. 

Our imcoming emails are from Site A which are then transported to Site B where i'm sitting. However i'm suspecting that due to the high CQL, all the emails are still stuck in Site A. So my question is whether can i suspend the database copy from Site A (Active) to Site B (Passive). Then maybe after end of business day, then resume the copy again. 

However I'm not sure if by suspending the copy, can the incoming mails which are stuck in Site A not be able to reach Site B.

Hi Wang,

Please post it here.

Technet forums - Previous Versions of Exchange - Microsoft:

https://social.technet.microsoft.com/Forums/exchange/en-US/home?category=exchangeserverlegacy

Are you saying your WAN link overloaded hence you are thinking of disabling the DAG replication traffic to allow transport to work correctly?

Other than that I don't see any relation of emails getting stuck and DAG.

Point to be noted is before you can suspend SiteA(Active copy) you need to switchover it to SiteB or if replication traffic is the case, simply suspend SiteB(Passive Copy itself)

"However I'm not sure if by suspending the copy, can the incoming mails which are stuck in Site A not be able to reach Site B."

It has nothing to do with DAG replication, email will always flow to the ActiveCopy, suspending it will not necessarily move the emails to SiteB. You should looking into what is causing the performance bottle neck.

References:

Suspend or Resume a Mailbox Database Copy:

https://technet.microsoft.com/en-us/library/dd298159(v=exchg.141).as

Hi WZ.Wang,

Thank you for your question.

Q: my question is whether can i suspend the database copy from Site A (Active) to Site B (Passive). Then maybe after end of business day, then resume the copy again.

A:  By default the sync of database is real-time, you could suspend copy and sync it out of time. However, we suggest the sync of time is real-time. Because the data will lost when then active node is destroyed and the database is not synced. 

As my concerned, if there are active database node in site B, the incoming emails will be delivered to site B without any problems if you suspend the database copy in production time. 

If the queue length is more than 10000 and email get in struck, we suggest you check the database copy and the bandwidth of MPLS between site A and Site B.

We could refer to the following link:

https://technet.microsoft.com/en-us/library/dd351258(v=exchg.150).aspx 

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim