Invalid Global DNS name and sendmail

[Andrew Fremantle]

Thanks to everyone who replied, the solution is detailed below

Copy /usr/share/sendmail/cf/domain/generic.m4 -> /etc/mail/custom-domain.m4
softlink /etc/mail/custom-domain.m4 -> 
/usr/share/sendmail/cf/domain/custom-domain.m4
Edit /etc/mail/custom-domain.m4 and remove the EXPOSED_USERS('root') line
Edit <hostname>.m4 and change the DOMAIN(generic) line to 
DOMAIN(custom-domain)

Somehow this broke Make, so I ended up having to manually nuke 
<hostname>.cf and <hostname>.submit.cf to force it to rebuild them.

Then a simple "make install" followed by "make stop; make start" and the 
mail began to flow.

That allowed my previous masquerading configuration to work correctly, 
and I'm now getting my periodic emails.