Hoople - 12:08 am on Nov 22, 2010 (gmt 0)
I call them on the telephone. Sometimes you have to call a few times to get someone willing to transfer you to 'the email guy' or IT in general.
Too many times the postmaster account and the abuse account DOES NOT exist on the mailbox server. The postmaster account and the abuse account are required by RFC [faqs.org]. By default they are not implemented by MS Exchange!