Very! Those you communicate with will be looking at your e-mail in its entirety to determine your overall tone. For example, if you send a terse e-mail and sign-off with “Have a nice day!” then it is clear that you intended to be sarcastic and the recipient will learn a bit about the type of person you are. The point here is that without a doubt your sign-off can portray the overall demeanor behind your e-mail.
Most folks stick with the standard:
The above is not anything unique or special and will be viewed that way. Recipients will know that is what you automatically append to all e-mails. So use the opportunity you have with a sign-off to ensure your point, purpose and customer service goals are apparent.
Your sign-off need not be standard and customary. Nor does your sign-off have to be relegated to a word or phrase above your name like the three examples above to add to your e-mails overall impression. For example:
HTH! (Hope this helps!)
Have a great day! (Only if sincere.)
Thank you so much!
Talk to you soon! (TTYS)
Look forward to hearing from you! (When you are soliciting a response.)
Let me know if you have any questions…
Your sign-off gives you the opportunity to ensure that the sentiment of your e-mail is clear and not open to interpretation or the recipient’s speculation as to what you want to accomplish or what is expected of them. Always take advantage of and use this opportunity wisely!