Hi again.
Dear Messrs. would probably do...
Sorry, definitely not. That is rarely used, and really only with multiple surnames.
If I want to write a very stiff and extremely formal letter to a law firm that I don't like, I might address them as
Dear Messieurs Smith, Jones and Gradgrind,
It seems that a lot of Forum readers feel very, very uncomfortable with the idea of not starting with a formal salutation, yet in email I would say that this is more or less the norm for native speakers.
Perhaps this lack of comfort is a reflection of differences in cultures, where other cultures are more formal. Other manifestations of this difference,in other threads, seem to include, for example, almost a big fear by people that they will seriously offend a woman if they accidentally address her as 'Dear Sir'.
I should add that in starting all my posts here with 'hi' and ending with 'best wishes', I am very much in a minority. I just started doing that for fun, and it has become a little unconscious ritual. It's not what many people typically do.![Smile [:)]](/emoticons/emotion-1.gif)
Best wishes, Clive