Weird things in the mail queue

I noticed a mail stuck in my mail queue. dovecot-lda was returning error 64 Invalid parameter given. (EX_USAGE).

Weird, weird, weird. After some sleuthing, I found the sender address was FirstLast@domain.tld, with a UTF8-encoded Unicode U+FEFF ZERO WIDTH NO-BREAK SPACE character (AKA byte order mark) between "First" and "Last" :)

Since that is passed as the -f parameter to dovecot-lda, it was giving the 64 error.