Bounce or trace service failure?

One of our users has just sent out a mailshot to 450 recipients.. not a
common occurence by our usual standards.

Whilst most have been delivered, or deferred for the "usual" reasons, I have
a few that are visible via mailq as "(bounce or trace service failure)".

I'm running Suse 9.0 with the latest snapshot from Carsten Hoegers Suse
rpms.

I know things like this are usually logs logs logs, but i'm having trouble
knowing exactly which bits are relevant, this is a line for one of the
recipients with this status, i'm hoping obscuring the email/ip doesn't
matter too much -

Jan 27 08:34:35 relay postfix/smtp[23359]: 256EB6155:
to=<someone@somedomain.com>, relay=mail.somedomain.com[1.2.3.4, delay=33,
status=deferred (bounce or trace service failure)

the domain is valid and has MX records, though from a quick look through the
logs for previous mail to this recipient it would appear the local part may
not be valid.

TIA for any pointers,

regards,
Paul
--
Paul Hutchings
Network Administrator, MIRA Ltd.
Tel: 44 (0)24 7635 5378, Fax: 44 (0)24 7635 8378
mailto:paul.hutchings@mira.co.uk