no, that is wrong, where did you find it?

Bart + Paul - there is a movement abroad to have every piece of written or spoken language 'adapted' to the demands of feminism. while in some cases this is to be greeted, in others it just appears ludicrous.

Dear Sirs and/or Madams is the traditionally used phrase, and, while there is no 'common sense' need to change this, it is certainly one of the more harmless changes.

since, even today, there are considerably more men in business than women, the phrase in the order sir/madam has managed to maintain its place, and I'm not very convinced that the cause of feminism is being well served by putting Madam first...

I would also say it is very rare to use this expression in the plural and

Dear Sir/Madam

will nearly always be sufficient. ButI agree, Sir first. (P.S. I am a woman and take no offence at the expression!)

May I just add that it is most common to write "Dear Sir or Madam" OR "Dear Sirs" OR "Dear Madams" but not "Dear Sirs and Madams" - although the former is more correct, since if you are not using the person's name, you cannot know whether you are writing to a man or to a woman and therefore have to address both sexes.
Dear Sirs and Madams makes a total of 441 hits on UK sites, the ones I looked at were poorly written applications by non-native speakers.
I hate to correct odondon irl. since his/her comments are normally excellent (even about peat cutters! ;o) ), I presume your answer should have read "Dear Sirs and/or Dear Madams and/or Dear Sir or Madam (I personally have never heard Dear Madams, - which doesn't mean it doesn't exist, just that it sounds funny to me).
I sometimes wonder why this salutation gets so altered, I wouldn't bother changing the German to Sehr geehrte Herr und Dame, so why does the standard English phrase get changed??
I would also add that if you know the person's name you MUST use it, it is impolite to then write Dear Sir or Madam