What is your opinion on using "Dear All," in business emails when addressing to a group of people? Is this too informal? Or has it been an accepted usage?

The situation is that I know all the recipients but I can't find a simple term that can represent all of them. The recipients include my colleagues and external parties. There are a number of alternatives but I think none of them fits in the situation.

Dear Sirs - sexist
Dear Ladies and Gentlemen - seems too formal and outdated
Dear Colleagues - not all of them are colleagues, some are external parties
Dear (name of committee, etc.) Members - not all of them are members

Do you have any other suggestions?

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Comments  (Page 2) 
Just a small point.

When using 'Dear all,' please use lower case for the 'all' and not 'All'.

The word all is not a name and doesn't warrant the use of a capital letter.
 anonymous's reply was promoted to an answer.
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An oldie but goodie always does the trick with this one. It is: "To whom it may concern."
Why not saying To whom it may concern
"To whom it may concern" is not suitable in this case, first because it sounds too formal and too indifferent, second it sounds like a superior is adressing his subordinates, third the writer seems to know who exactly he is writing to and all the people are liked to be concerned, so where comes the "may"?
Is 'hello, my partners' or 'hello, my friends' an alternative?
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 BarbaraPA's reply was promoted to an answer.
And these are not normal: 'hello, my partners' or 'hello, my friends'.
i agree with you, it is the style i using for long.
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I use ' Dear team " & it works well for me
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