How should you end a professional email?

Hello Miles!

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  Formal tone
  Using a formal tone will enhance the professionalism of your emails by conveying your respect for the email recipient’s position. This includes avoiding contractions and slang and being sure to use polite terms, such as “please,” “thank you,” “sorry,” “apologies,” “if possible,” and “at your convenience,” where needed. Your professional emails should also be well structured, with an opening and a closing bracketing the body of the message. In particular, you should begin your emails with “Dear” rather than “Hi” or a similar informal greeting, and formal closings may include “Sincerely,” “Thank you,” “Best wishes,” and “Best regards.” Depending on the context, and particularly if you have never met the person before, you should err on the side of using his or her title and last name (such as “Ms. Arc,” “Mr. Arc,” “Dr. Arc,” or “Prof. Arc”) rather than just the first name or the full name; only once you have been told that it is permissible to use the recipient’s first name or once the recipient has signed his or her first name to a response should you consider using this more informal greeting.

  
  


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  Concise writing
  The people to whom you may be writing are likely busy with teaching, research, and/or administrative work, so it is best to be concise and to the point to convey your respect for their time. This includes avoiding the common pitfall of spending time stating your name in the first sentence; your name will be signed at the bottom of the email, so this step is unnecessary. If possible, limit your message to only a few sentences, mentioning who recommended that you write (if applicable), briefly describing your background if the person is not familiar with you, clearly stating the purpose of your email and the expected next step (often a request), and thanking the individual for his or her time. As a result, the body of an effective professional email could be as brief as 2-5 sentences long. Note that the subject line should also directly reflect the purpose of your email.

  
  


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  Example
  One common situation is a first- or second-year graduate student needing to contact a professor regarding learning about the professor’s research and potentially joining his or her research group. This can be a particularly intimidating circumstance, especially if the student is new to research, the researcher is prominent, and/or the student has never met the researcher before. Here is an example of a professional-sounding, concise email that could be written in this case, consistent with the tips provided above:

  
  

Subject: Meeting request

Dear Dr. Arc,

Dr. Aje recommended that I contact you. I am a first-year graduate student in immunology with an interest in innate immunity. If possible, I would be interested in learning more about your research and potential rotation opportunities in your research group. Please let me know if you would be available to meet sometime next week.

Thank you,

Stu Dent

I hope the tips can help you. Best!

Source: http://www.aje.com/en/arc/editing-tip-professional-email-writing/

I think when writing a professional email it's very important to be concise with what you're saying but also remain conversational. This helps to build relationships but also remains considerate to people's time. I find I end my emails professionally with "Best, _______", "Sincerely, ______" or "Thanks, _______" depending on the contest of the email. Hope this helps!