My pet peeve is emails that do not include contact information from the sender. Of course, it is easy to reply to emails; the issue is when follow up requires either a phone call or sending something. And yes, in most instances, I can look up the phone number or mailing address.
However, if people would just include a detailed signature in each email they send, it would make my life (and the lives of countless millions of people) easier.
So, please, include your contact information in your emails.