Wife of a 24-year veteran letter carrier here. I’ve been mailing checks to pay bills for years now, some of them for huge amounts like for $2,000+ Discover card bills, and some of them incredibly important, like for mortgage payments, and have never had a single instance of having a check disappear in the mail.
You don’t even have to send it registered or certified mail. Just make sure there’s a legible return address, make sure the address itself is legible and correct, and don’t forget to put a stamp on it. Wrap it up in a piece of paper (doesn’t have to be a whole wad) so it’s not quite so obvious it’s a check.
If you’re just worried about the recipient getting the money, and not necessarily about someone stealing it in transit, then go ahead and send it either registered or certified. But ordinary first class, in my experience, works just fine.
According to the Better Half, postal thieves in the line of processing basically scan for birthday cards, which are easy to recognize by their size and shape, and which are statistically more likely to contain cash. They’re not interested in plain business envelopes.
But if somebody did intercept a check and try to cash it, then that would be a criminal proceeding, and would be the problem of (A) your bank, (B) the place where he cashed it, and © the Postal Inspectors, who, trust me, you do not want to have mad at you. Seriously.
Paper checks are actually safer than using plastic, because they leave a paper trail. Whoever cashes a stolen check leaves a trail of evidence behind him, such as a signature, sometimes a driver’s license or other ID, sometimes a picture on a surveillance video, whereas using stolen plastic is like finding money in the street.
But like I said, the Bad Guys who are sitting there scanning the flow of mail for something to steal aren’t interested in plain business envelopes, because there are just too many of them, and because they know it’s too much trouble to cash a stolen check, and that it leaves a paper trail.
Really, just stick it in an envelope, wrap it up in your choice of humorous Internet web page, and mail it. It’ll be fine.