> 1) Is there any way of stopping people using my domain in a 'from'
> address? (I'm guessing not)
http://hantslug.org.uk/cgi-bin/wiki.pl?WhatIsSPF
> 2) Does this mean our domain will get listed as a spammer?
Possibly. Most blocklists are quite savvy about this sort of thing, so
will tend not to list you - but bayesian filters (e.g. SpamAssassin) will
tend to score you as spam if they see lot purportedly from your domain...
HTH
Vic.