[BlueOnyx:18673] Problems sending to Plus Net - any ideas please?

[Colin Jack]

Ideas please. I am flummoxed.

We are suddenly struggling to send mail to plus.net domains from all our BX servers.
The odd one goes through but the majority don't - just timeout and get deferred until they eventually die.
Plusnet say they haven't changed anything and neither have we. They can't see anything their side (they say).

This is typically what happens:

<mailuser at plus.net>... Connecting to mx-ironport.core.plus.net. via esmtp...
220 avasin04.plus.net Plusnet Cloudmark Gateway ESMTP server ready
>>> EHLO server2.mainline.co.uk
250-avasin04.plus.net hello [188.39.8.117], pleased to meet you
250-SIZE 104857600
250-8BITMIME
250 OK
>>> MAIL From:<user at domain.co.uk> SIZE=36697
250 <user at domain.co.uk> sender ok
>>> RCPT To:<mailuser at plus.net>
250 <mailuser at plus.net > recipient ok
>>> DATA
354 enter mail, end with "." on a line by itself
timeout writing message to mx-ironport.core.plus.net.: Resource temporarily unavailable

Sending to anyone else is fine - including 'fussy' servers like AOL and MessageLabs.
Sending to Plusnet from the command line on our server works fine.

Anybody any ideas please?