Some small bug fixes in smtpserver.rb

Hi, guys. Would you like to merge some little bug fixes for smtpserver.rb I made several years ago? I'm going to destroy my eventmachine fork in two weeks. That means, my little work on smtpserver.rb is going to be void, if it'll still unmerged, since no one is interested in it. ;-)

Greetings,
Averell