03-13-2006, 02:16 AM
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As per the recommendations by RIM.....the latency between the BES and Mail servers should be <35ms, and the BES and Mail servers should be on the same LAN. If you expect to have a large # of users at respective locations (remote sites), then it may be preferable to have a local BES to facilitate those users.
The BESAdmin service account is used to monitor the users mailboxes for new updates and also the BlackBerry Messaging Agent (see MAGT logs) is used to provide email, calendar, address lookup, attachment, and wireless encryption key generation services.
As for the config db, it's ideal if the SQL db is central to all the BES in the environment. That way if one BES goes down, then users can be "moved" over to another BES without incident (seamless/transparent to the users).
If the SQL db goes down, it only affects moves, add or changes as far as new users or existing users are concerned. That is, you'll not be able to add/modify a user, create/modify IT policies, or any other administrative tasks on the BES. If you should restart the BES during this situation, it'll not start the Dispatcher service and all users will be negatively affected.
If the WAN link goes down, then monitoring of the users by the BESAdmin service account will be stopped. The only messages that they'll receive are those in the "pending queue" and those already sent to the wireless network (described as "sent" in the logs). PIN-to-PIN will work...useful in emergency cases, but not practical in business-related cases.
The latency described above affects mail redirection....this translates into mail delivery delays. It all depends on how tolerant your users are with respect to mail delivery on the devices. A good test is to send mail (from any fat client) to a user's device with the <config> option in the subject line and see what the return (round-trip) timestamp indicates. This would give you an indication of the time it takes for a user to receive a message(s) on average.