1) Writing in all capitals can convey that you are shouting in your message, and nobody likes to be yelled at. Consider other ways to get your message across while conveying its importance. Using all capitals can be annoying and trigger an unintended response.
2) When sending a mailing, some people place all the e-mail addresses in the To: field. If the recipient list is large, that means that all your readers will have to scroll through the list of those on the e-mail to read the message. In the case of viewing e-mail on a smartphone, this can be extra irritating. You also have to consider that others may not want their e-mail address published for everyone to see. You can avoid both these issues by using the BCC field, or using a program like Outlook to do a mail merge that sends a unique message to each person on your list.
3) E-mail messages are easy to copy, print and forward. If you don’t want anything getting out, don’t e-mail it. Plus, remember that even if that e-mail isn’t forwarded on to someone else, company management can easily intercept inappropriate mail.
4) Save abbreviations like LOL (laugh out loud) or IDK (I don’t know) for text messages among friends. Some may not understand your abbreviations. And while emoticons are fun, they just aren’t professional and you don’t know how the recipient will take them. Just like abbreviations, readers may not know what they mean. It’s better to spell it out and write what you mean.
5) This will almost always annoy your recipient before he or she has even read your message. Besides, it usually does not work anyway since the recipient could have blocked that function, or his/her software might not support it. If you want to know whether an e-mail was received, it is better to ask the recipient directly to let you know.