rcmail: pass smtplib.SMTP.sendmail to_addrs as list Passing it as a set worked ... but is apparently wrong. The documentation states it has to be a "list of addresses". Pytype warned: File "kallithea/lib/rcmail/smtp_mailer.py", line 99, in send: Function SMTP.sendmail was called with the wrong arguments [wrong-arg-types] Expected: (self, from_addr, to_addrs: Union[Sequence[str], str], ...) Actually passed: (self, from_addr, to_addrs: set, ...)