Cannot send mails this morning - via phone, webmail or Tbird.
Tbird error message is -
An error occurred while sending mail. The mail server responded:
4.1.1 s2gLbZvb9HGLw Too Many Recipients (TT501).
Please check the message recipient "<email address removed by me>" and try again.
Which is garbage because there's only 1 recipient, and a known good address.
Webmail just gives the fantastically unhelpful "Failed to send mail" blue bar.