Hi there,
Every time I do maintenance to either my domain controllers or mail servers (one or the other, not both at the same time) Add2Exchange stops working and logs an error such as Collaboration Data Objects - MAPI_E_FAILONEPROVIDER and AgentDirector failed to log on in the Add2Exchange event log.

I understand the application stop working for a while, but last time I figured out it stopped working for 3 days, and without my intervention it would had remained in that state.
 

Answer:  ANY time you do maintenance on your Domain Controller or Exchange boxes, OR THE REPLICATION SERVER ITSELF you should stop the Add2Exchange Service on the replication server. I believe there are shortcuts to the “Add2exchange Service Stop” utility on your desktop, but if not, this reference should get you there: Stopping A2E during antivirus scans or backs so service doesn't freeze.

The Add2Exchange Stop utility stops the Add2Exchange Service, tests to see if it is done, and then Stops the A2ESQLSErver instance. If you do not reboot after, you should run the Add2Exchange Start Utility to start both components of Add2Exchange. Starting the Add2Exchange Service does not start the A2ESQLServer, and there will be errors in the Add2Exchange Event log stating this and how to correct – by starting the A2ESQLServer instance and then restarting the Add2Exchange Service.

A2E works when all the pieces are in place and in order. Doing an Microsoft Update on your domain controller stops A2E from being able to do lookups and verify credentials. I don’t know of too much software nowadays which will work without that piece. Also, when you do Exchange upgrades and reboots, doing this “rips the rug out from underneath us” because it often dismounts the store and always requires a reboot (even if they don’t tell you to) and Add2Exchange can stay in that state until you do the procedure below. Following this start and stop of the Add2Exchange Service procedure will ensure proper replication and not surprise you when it hangs for a period of time or gets “provider fail” messages. From its point of view, there is no provider to provide for us.

Dealing with your situation, once your systems are back in place and available, please make sure in TaskManager of your replication server, the Add2Exchange Service is not running, and check for the A2E Director.exe and A2ESP.exe Director, the Add2Exchange sync helper programs. If the Add2Exchange Service is not running and the A2ESP and the A2E Director are in memory, (this is the only time I recommend this) please end those 2 tasks and then start the Add2Exchange Service again normally. After the A2E Service is started, the Service will wait 60 seconds and the Calendars sync will attempt to run by loading the A2E Director. If there are no relationships, it will drop without loading the A2ESP. If there are, the A2ESP will load and sync, then drop, and load another one until there are no more. Then, Add2Exchange Service will wait 60 seconds and then load the Director and see if there are any Contact relationships. If there are, then it will sync those. If not, it will wait 60 seconds and then try to sync Tasks, and after that, Add2Exchange will sync according to the schedule you set up in the Add2Exchange Console under the Services Utility tab. In the Enterprise Edition, you have the ability to turn off Syncing of folders you do not have any relationships for or you want to pause for some reason. A2E Enterprise syncs by default, the Global Address List Cache, Relationship Manager (for templates) Notes, Calendars, Contacts, Tasks, Posts and then Post it Notifiers, waiting 60 seconds in between each, and then syncing from then on as per your defined schedule.

Hope this helps