how to mail rent increase notice

[Nadia Alrawi]

Hi, I have owned rentals for several years and have never had any major issues. "Knock on wood"....Nevertheless, I am starting to try and make things more official and would like to hear opinions on sending out rent increase notices. I have previously just mailed them out by normal mail and it has worked fine. But do any of you actually send them out via registered mail to show proof of postage in case one day we get "that tenant" who claims he hasn't received the notice...thanks for the input....