Thomas, you fountain of widom you. YES, you have solved the problem.

I upped the MercuryE timeout to 300 seconds and it WORKED! My test message ot 1334 bytes took 203 seconds to be delivered, but delivered it was.

Many many thanks

Has someone out there seen something like this:

Our mail delivery to valid addresses to a certain Microsoft ESMTP server via MercuryE is consistently failing. All other domains accept our email and the sysadmin on the other side says that we are not on any blacklist and that all other mail to his server is arriving OK. We are both at our wits end:

MercuryE logs show the connections to the primary and alternate IP's are failing:

9:54:42: processing job MO00107D
Resolved MX for 'unisa.ac.za' to 163.200.219.16
Connecting to 163.200.219.16
Connection error.
Attempting connection to alternate, 163.200.219.15
MAIL FROM:<pbeddy@treverton.co.za>
RCPT TO:<davel@unisa.ac.za>
  Network or protocol failure after RCPT TO with 163.200.219.16
TCP/IP error during processing.
9:56:04: 82 seconds elapsed, closing connection.

 When I try a telnet session to their port 25 from our Mercury box, all appears to be well:

Traceroutes from my server fail a few hops before  reaching there, but his traceroutes reach me without fail.

 A verbose session log from Mercury:
15:38:05.578: --- Tue Feb 17 15:38:05 2009 ---
15:38:05.578: Connect to '163.200.219.16', timeout 60.
15:38:07.593: >> 220 umkn-edg02.int.unisa.ac.za Microsoft ESMTP MAIL Service ready at Tue, 17 Feb 2009 15:38:07 +0200<cr><lf>
15:38:07.593: << EHLO server.treverton.co.za<cr><lf>
15:38:09.468: >> 250-umkn-edg02.int.unisa.ac.za Hello [196.30.42.3]<cr><lf>
15:38:09.468: >> 250-SIZE 10485760<cr><lf>
15:38:09.468: >> 250-PIPELINING<cr><lf>
15:38:09.468: >> 250-DSN<cr><lf>
15:38:09.468: >> 250-ENHANCEDSTATUSCODES<cr><lf>
15:38:09.468: >> 250-STARTTLS<cr><lf>
15:38:09.468: >> 250-AUTH<cr><lf>
15:38:09.468: >> 250-8BITMIME<cr><lf>
15:38:09.468: >> 250-BINARYMIME<cr><lf>
15:38:09.468: >> 250 CHUNKING<cr><lf>
15:38:09.468: << MAIL FROM:<postmaster@server.treverton.co.za> SIZE=510<cr><lf>
15:38:09.734: >> 250 2.1.0 Sender OK<cr><lf>
15:38:09.734: << RCPT TO:<davel@unisa.ac.za><cr><lf>
15:39:09.734: 8: Socket read timeout
15:39:09.734: << QUIT<cr><lf>
15:39:16.156: >> 250 2.1.5 Recipient OK<cr><lf>
15:39:16.156: --- Connection closed normally at Tue Feb 17 15:39:16 2009. ---
15:39:16.156:  

Any ideas would be much appreciated.

Our mail delivery to valid addresses to a certain Microsoft ESMTP

server via MercuryE is consistently failing. All other domains accept

our email and the sysadmin on the other side says that we are not on

any blacklist and that all other mail to his server is arriving OK. We

are both at our wits end.

The first thing I would do in to increase the MercuryE  timeout from 60 seconds to more like 300 seconds.  It will not help in this case but a server should not be giving up in 60 seconds.  Second, I'm trying to send a test message to the same guy to see if this is somehow a common MercuryE problem. Just checked, my message seemed to go right through without any problems at all.

FWIW, it does appear the the receiving server is breaking the connection as soon as it sees the RCPT TO: address.  Does this same thing happen when you send postmaster to postmaster? In any case it really does appear that there is something on the receiving side blocking you connection.  This happens a lot with MercuryE and the anti-spam systems especially if MercuryE is using a randomly assigned IP address or a rDNS (PTR record) that is different than the EHLO string.  Now you have multiple PTR records and that's perfectly valid but their query may not like it.  Not sure why you have PTR records for non-SMTP www host names though.

Answer Section:
    2.42.30.196.IN-ADDR.ARPA, PTR, www.thecouchhouse.co.za
    2.42.30.196.IN-ADDR.ARPA, PTR, www.thecouchhouse.com
    2.42.30.196.IN-ADDR.ARPA, PTR, server.treverton.co.za
    2.42.30.196.IN-ADDR.ARPA, PTR, treverton.co.za
    2.42.30.196.IN-ADDR.ARPA, PTR, www.mine-site.co.za
    2.42.30.196.IN-ADDR.ARPA, PTR, www.mine-site.com
    2.42.30.196.IN-ADDR.ARPA, PTR, www.treverton.co.za