The following post is from a great website called dontquityourdayjob.net.
The Email Subject Line is Important
Submitted by Joann on September 28, 2009
Emails that lack subject lines, or have generic one- or two-word subject lines, are frustrating to receive. Many of us get hundreds of emails a day. Non-specific subject lines are time-wasters for email readers who are sifting through many emails trying to pick out the urgent and actionable ones.
Write something specific in the subject lines of the emails you send. Tell your reader the gist of the message and the action you expect. Many readers sift through emails on handhelds and detailed subject lines facilitate out-of-the-office reading and responding. Your emails will get quicker attention and faster responses. And you may be surprised at your own ability to distill your message into a short phrase.
I totally agree with Joann! I would also add from a technical standpoint that email filtering programs will frequently block emails that lack subject lines or have subject lines that have been associated with viruses. These include, “Hi and Check It Out”.