As a female that handles much correspondence on a daily basis, the one thing that irks me is to see “Dear Sir” or “Dear Sirs” (or “Gentlemen”) as a salutation. This is email sent blind to a company which the correspondent would have NO idea who they might reach, female or male. Now I’m not what I would consider to be a feminist, but there is also NOTHING about me that is sir-like.

Having access to contact information of the individuals using the salutation inappropriately, I know that most are people outside of the United States (although there have been some from the U.S…at least using U.S. addresses). I realize that it’s probably more of an issue of ignorance or influences of their own culture or generation (or combination thereof). Doesn’t change it from being offensive, however.

You would think that it would be more of a “male” faux pas however, in my experience, it seems to be committed by females just as often…

sir–

encarta.msn.com

salutation in letter: used at the beginning of a formal letter to a man, especially one whose name is not known to you ( formal )
Dear Sir

ultralingua.net

1. Term of address for a man.

http://www.wilbers.com/FAQSalutations.htm does a fine job in summing this up (emphasis added by me):

10. Is Dear Sir correct?

Dear Sir is acceptable when addressing a male reader or a group that you know to be all-male, though it sounds formal and perhaps old-fashioned, as noted above. It should not be used to address a group that may include both males and females. Instead, use Dear Sir or Madam…

Also, to bring the point home–

Office Survival

In the United States, it is an bad idea to use “Sir” or “Mr.” unless you are absolutely certain that your correspondent is male.

Just, please, leave it at “Hello” and no one gets hurt… 😉