It depends on the professional culture. Some are more formal, and thus "Dr. Jones" would be most appropriate. Others are much less so, and either "Tom" or "Yo, dude" would be just as acceptable. Listen to what others are doing, and if in doubt, err on the side of politeness until invited otherwise. In a foreign language, use the formal address (Sie, usted, vous) until and unless invited to use the familiar forms.
In particular, be careful being too chummy with senior colleagues. They may say immediately, "Good heavens, don't call me Dr. Farnsworth, call me Hubert!" but let THEM extend the invitation to YOU!
Dear Esteemed Colleagues
What is the proper salutation for a register of wills, e.g. Honorable John White?
The proper salutation for a probate judge is "The Honorable [Judge's Full Name]."
The proper salutation when writing to a judge is "Dear Judge [Last Name]" or "Your Honor."
the correct salutation for two men is Messrs
Hello.
Your Honor
Dean actually is the proper salutation. One could say: Dean Redmond, would you please sign this form? Alternatively you could just use the Dr. salutation or the Professor salutation if those are appropriate, which they generally are.
The proper salutation for a doctor is doctor or professor depending on their title. In writing the short form can be used which will be Dr. or Prof.
A proper salutation for greeting the president of a business is "Dear Mr. President". To conclude a letter, the proper word is "Sincerely" and a the name of the writer.
miss
Miz.