Sendmail questions

[John P. Marr]

   I have been looking at the sendmail manual in RH Linux 6.0 trying to 
figure out just what it does.  As far as I can understand, it only sends 
pre-formatted messages somewhere. Could someone please explain to me just 
what sendmail does, and why when I boot linux now the system hangs at 
sendmail? Could it be because I changed the host name or something along 
these lines?

Any comments are welcomed

John