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SMTP cannot resolve


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Any suggestions on what may be happening are helpful..


PBXnSIP windows Server with IP x.x.x.250 no longers relays mail via x.x.x.6 Exchange email server.


From the PBX a full telnet email session can be sent via Telnet and the Exchange server successfully sends these emails.


the PBX log has the following entry a na few moments later the error


Sending CDR email to <test email address>

SMTP: Cannot Resolve



Wireshark traces do not reveal any SMTP packets, meanwhile the 40+ phones and all calls are being handled fine... The PBX service has been restarted and no change to the symptoms. We'd like to reveal the cause if possible. A total system restart is planned, but not very hopeful as SMTP work fine with telnet to the exhange server...


Any Deep Thoughts? - Cheers.

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The Mail Server entry is in fact x.x.x.6 as the mail server entry.

From windows or command prompt an SMTP test tool and command line works fine, proving the Exchange server x.x.x.6 accepts and relays the mail.

We made a hosts file entry for mail.domain.com and changed the mail server entry and the same results.

Pinging by name or IP operates fine.



What did you mean by including an "@" ?



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What did you mean by including an "@" ?


Well, maybe you accidentially used a server name that includes a "@" (as in account@server). Then the PBX would try to find the DNS entry for account@server, which obviously fails. Okay, would be stupid. But all problems are stupid!


Apart from that, seems it is time for Wireshark and trying to find out what is going on.

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All Things are possible. - but this one is narrowed down to PBXnSIP

The Local Raid controller can successfully bounce mail off of the Exchange Server using the same mail settings set in the domain settings.

Outlook Express Will Successfully Send email using the same settings as below.

The PBX executable is MD5 the same as the original executable in a local folder

We easily capture and display SMTP, ARP traffic when either of the above programs send email but the PBX application makes no attempt to communicate on the LAN segment...

The wks dns cache correctly identifies the mail server by ip address

A full restart fails to resolve

The minimum # of windows services are running...

Viewing the TCP connections the PBXctl process never attempts to connect on port 25

really Strange and after 5 hours of analysis, the log still reports SMTP: Cannot resolve.

we are convinced it's now time to reinstall // update.. Successfully been running for some time, and this problem surfaced several weeks ago....


I hate not knowing the exact cause of a trouble but in this case, I know the shortest distance to the end goal is likely now to be the reinstall.... Yuck , but we'll improve on the overall system in the process...



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