Someone mentioned before about hosts.allow and deny
Seeing as I'm denying everything in hosts.deny I had to put in hosts.allow
to allow access.
Just about the only other things I changes in sendmail.cf was this line:
O DaemonPortOptions=Port=smtp,Addr=192.168.1.100,127.0.0.1, Name=MTA
Although I did the bad thing and edited it manually after making a backup of it
Apart from that just the usual entries in the access file for relaying got it working for me.