If you have a short message to send you can save yourself some time by putting the whole message into the subject line.
This is also better for the receiver since they do not need to open the message unless/until they are going to reply to it.
The trick here is to use the abbreviation EOM at the end of the subject line. EOM means end of message.
Subject: Please send the revised budget figures by Friday. Thanks. EOM.
Subject: For info: Latest version of Project X report. EOM