:swoosh_sender swaps from and reply_to in Swoosh email construction, and removes reply_to.
A literal list reply_to value is not changed into from, because Swoosh.Email.from/2 accepts a
single mailbox while reply_to/2 may accept a list. The removal has no such restriction: a
reply_to(email, value) call collapses to the email (a piped stage to what was piped into
it), and the reply_to: option in Swoosh.Email.new/1 is dropped — replies then silently go
to from.
No from removal is generated: Swoosh validates the sender at delivery, so that mutant would
fail validation without testing assertions about the sender.