Sendmail was working properly prior to any of my poking around. In the past, I had made changes to sendmail.cf directly, bypassing sendmail.mc entirely. But for reasons unknown I broke from convention and decided to follow some advice to use the sendmail.mc file to make changes. In the process of this, I managed to lose my old sendmail.cf file.
I was making changes to sendmail.mc and when I ran m4 sendmail.mc > sendmail.cf a vague error was encountered:
NONE:0: m4: ERROR: end of file in argument list
And my old sendmail.cf file was overwritten. Now I can't restart sendmail without interrupting email to/from the server. Can anyone help me out here?