Believe it or not there is a reason behind every “rule” agents have when it comes to querying. The reason isn’t to make your life crazy, but to help give you a better shot on the road to publication.
On the BookEnds website we advise all authors to put the word “query” or “submission” in the subject line of their query. The reason for this is that we’ve set up our spam filters to push those words through. If “query” or “submission” come up in the subject line my server knows not to mark it as spam and push it through, and my email manager knows not to mark it as spam and to file it automatically in my query folder so I can read it later.
Believe it or not there is a reason for our madness.