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Dear Ladies and Gentlemen - seems too formal and outdated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 6) 
Dear All
"Dear all" is absolutely conventional and correct usage for the scenario described by the poster. It is appropriately formal for an e-mail in business English. "Hi everyone" is indisputably less formal! So you might use "Dear all" for (say) a Department-wide e-mail or a relatively formal e-mail to colleagues and external parties; and "Hi everyone" to update perhaps a smaller team of colleagues whom you know better. Also the former might be better for an e-mail of greater importance (eg re data security) and the latter for organising a team social.
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