Multiple Exchange Servers With UM / Voicemail

[Shadragon]

Good Day,

We have multiple Exchange servers as we have a large number of employees to support.

The UM is set up in Exchange per the documentation and is working for some, but we noticed that some people get an auto-disconnect when it is supposed to go to their voicemail. This appears to be because the mail server they use is not listed. In the Voicemail section, under "Exchange Server Hostname or IP" we can't seem to add multiple Exchange servers. The FQDN that is there is working, but we need to add another to cover the other half of the office as it does not transfer internally in Exchange.

How can this be done? Thanks.

 

[Shadragon]

OK, this was a problematic issue that involved Wireshark and a whole lot of testing. You can ignore my first post. There is no way to enter multiple Exchange servers in the 3CX Voicemail settings.

Here's the situation: When you have multiple Exchange 2016 servers hosting your users, 3CX will try to go to the named server (EX2 in our case) from 3CX voicemail settings using port 5060. By default, 3CX is set to use 5060 according to this documentation:

https://www.3cx.com/docs/how-to-create-impersonated-user/

If the user mailbox is not on that Exchange server, Exchange responds back to 3CX on service port 5062, not 5060, with a message that effectively says 'this user isn't on EX2, go to Exchange server EX1 instead.'

Due to the port disparity, the reply does not connect and the UM connection fails instantly. I'm sure 5060 would work as default with one Exchange server, but with multiple servers in a DAG it does not. We found this using Wireshark traces and when we changed the port to 5062 in 3CX Voicemail settings UM immediately started working for all users on both servers.

We're doing further work to make sure this fix holds, but several dozen test calls have been solid so far with the 5062 port set.