Had a problem with a client of ours, running Blackberry Enterprise Manager. One of the devices, a Blackberry 8820, stopped receiving any sync messages. Internet on the device kept working, and the internet e-mail account worked as well, but all communication between the BES and the device failed.

The first thing I did was to completely wipe the device, as I assumed there was a problem with the pairing between the server and the thing. But when I tried to reactivate it, it indefinitely hung on the first phase:

Quote

user@domain activating

As I was troubleshooting using the support site of Blackberry (where they explain the steps that occur when activating), I noticed that the activation e-mail sent by Blackberry SRP server arrived in the user's mailbox, and that it subsequently was retrieved by BES for processing. And then, it went blank.

So, something was going wrong with connecting back to the Blackberry device. The BES configuration tool showed no errors: the connection with SRP was working correctly, connections to the local database were okay, the service account was able to properly connect and retrieve mail from the Exchange account.
So, next up, was looking in the logs of BES. In our installation they were located in C:\Program Files\Research In Motion\BlackBerry Enterprise Server\Logs. I noticed BES logged extensively, which is very good when you're debugging this kind of problems. Anyways, as I was looking in the SERVER_DISP_01_20100108_0001.txt log, which contains the logging for the BlackBerry Dispatcher (the service that relays messages to the SRP), I noticed these errors:

[30310] (01/08 11:08:54.283):{0x2190} {User} Forwarding internal data to device, ...
[30375] (01/08 11:08:54.329):{0x2190} {User} Packet returned as FAILED - could not be delivered to device, Tag=

Well, that's interesting: the packet sent to SRP is bounced right back. This is starting to smell like a service provider issue.

So I called up the service provider, and explained the situation. He immediately told me that this was quite possible as this particular device was set up as an BIS-only (BlackBerry Internet Service) account. Well, that explains a lot.
They told me they were going to change the setting and that I had to wait for about an hour before retrying to activate, because the update of the account to BlackBerry itself could take some time. Also, I had to turn off the device completely (by removing the battery) to ensure the updated account info is succesfully downloaded to the device.

In fact, it took a little over 3 hours before Blackberry received changes made by the service provider. After numerous phone calls (and they claiming I really had to remove the battery, which I've already done for like 10 times), the error messages changed from FAILED to succeeded. Resetting the activation password, and have the device rerun the activation procedure, now worked, and the device started to sync again. Yay!

Conclusion

So, basically, if your sync mysteriously stops working, check out the logs. If it tells you that it can deliver the messages to the Blackberry device, it's most likely an issue with your service provider. Contact them first before all else.