This has come up before: http://postfix.1071664.n5.nabble.com/special-characters-in-mail-address-td47792.html
Short version: lots of outbound mail servers will refuse to *send* to email addresses with special characters. But at least when these posts were written, there was an option that turned off the ! handling in postfix: -Dan > On Mar 24, 2021, at 4:56 AM, Paul Fowler <pauldfow...@gmail.com> wrote: > > .
