Business communications don't have to be stuffy, but they should be professional.
One way to make sure you look super unprofessional in your written communications is to display overt excitement or extreme emotion about everything!!! Is the lunchroom out of coffee again!?! We have another design meeting this afternoon!!! I have to go to the doctor tomorrow morning!!!! I AM ON FIRE!!!!
These are all pretty banal things (okay, that last one could be pretty serious, but why are you writing about it?).
If what you're trying to convey is more important than it sounds, it's because you're not using all of your words.
HubSpot lays the ground rules for acceptable use of this useful but often overworked punctuation point in a chart aptly titled, Should I Use an Exclamation Mark?
Who should use this chart? If you've ever used two or three (or even more, shudder) exclamation marks together in a row, you need to check this out/ If your coworkers stop by to check on you after receiving your emails--or avoid you because they think you're angry all the time after reading your writing--you may have an exclamation mark problem. If email responses from your employer or colleagues include, "Tone it down," "Relax," or "Are you actually OK right now?" you just may be abusing exclamation marks.
Overusing this one piece of punctuation gives your communications a distinctly middle school flavor and kills your credibility. It makes you seem melodramatic and will give employers pause about allowing you to represent the company to partners or clients. You know, because you might freak them out!!!! Are you guilty of abusing exclamation marks in your emails, memos or even blog posts? Have a peek and see.