Which, if you used to use the blue boxes for mailing thin packages, is a huge annoyance because you can't anymore. :(
Seriously, these days nobody should be writing personal checks using a pen. If you do need a check for a transaction, use a cashier's check (different from a personal check, it's drawn on the bank) for occasional large amounts (like apartment deposit or buying a used car), or most banks allow you to send a paper check via online banking for routine needs -- you fill out the details online and it mails a paper check to the recipient that, AFAIK, can't be washed for check fraud. (All of this is USA specific, to be clear.)
[1] https://www.nytimes.com/2019/03/21/nyregion/mailbox-theft-fi...