Everyone has a word they hate or avoid. Some recoil at ‘moist’ while others detest ‘delish’. Pet peeves aside, words sent in emails cannot be taken back so choose them carefully and do not include the following words in any business communication, regardless of the context.
Sample :
Good morning Greg,
Thank you for your input [or attendance] at yesterday’s meeting. Consider the impression you are making on your colleagues with informal manners or gestures. Let’s keep our environment as professional as possible.
Sincerely,
Mr. Donovan

Hey
Business associates and clients are not your friends. They may be friendly, but they are not your ride or die friends. You can use this greeting in conversation, but when written down it is not acceptable. Hello is fine to use in a thread, but never as the opening salutation on a new email. Using ‘hey’ with the wrong recipient is akin to calling a teacher by their first name: insulting to a professional for its informal nature.

↓ Hey Mr. Donovan,
↑ Good morning Mr. Donovan,

Unprofessional
On a scale of one to ten, this word ranks at a twenty. Unprofessional is what can only be deemed as a fighting word. Using it to describe a person rather than their actions will result in an unpleasant and defensive response. People are worried about their livelihoods and this word casts judgement on their abilities.
↓You were unprofessional in the meeting today when you put your feet on the table.
↑Putting your feet on the table was not an appropriate action today at the meeting.
A situation can be unprofessional, but a person should not be called unprofessional unless you want to throw the gauntlet. There are a number of ways you can rephrase a sentence to avoid the word all together.

↓High-fiving people at meetings is unprofessional.
↑Consider the impression you are making on your colleagues with informal manners or gestures such as a high-five.

Awesome or trill
Everyone is desperate to appeal to Millennials to the point of detriment. Using their slang in business communications is not good for your professional image. Save it for personal emails. Good or great are the best adjectives to use in a business communication.

↓Your presentation was so legit trill today.
↑Great job on the presentation today.

Takeaway
Your words are you on paper. Consider your communication choices when expressing yourself to other professionals. Hey is too informal. Unprofessional is a word that will result in defensiveness, as it is quite judgmental. Save slang for your personal communications. Make the right impression with your words.