Indeed, it is /etc/sendmail.cf and it using the right one because I keep toggling it to try and get this working, otherwise all their outgoing mail would be frozen.
Do old versions of sendmail (this is 8.9.3) have different ways of doing these things ?
Why 8.9.3? There is an official Red Hat errata package of sendmail 8.11.6 for Red Hat Linux 6.2.
There may be slight differences in the sendmail.mc needed for 8.9.3 but I can't remember them off the top of my head. Could you post your sendmail.mc and the default one provided by Red Hat?
Paul.
