With the free plan I can receive mail to username+somestring@protonmail.com address, but if I reply to a message sent to this address I can't edit the sender field before switching to a paid plan. But if I switch plans are those sender addresses limited to any numbe? Note, I'm referring strictly to *username+somestring* (and *username+anotherstring*) style addresses, not to addresses that would contain different username part. Those are limited, ofc.