Hello,
on 2019/8/29 10:42, Andrew Bernard wrote:
421 Temporary System Problem. Try again later.
421 Try again later, closing connection.
421 Server busy, try again later.
The SMTP error 421 is normally used for temporary problems on the mail
server or a problem with the recipients email account.
Some mail providers might also return 421 after you reached a limit
(restriction) on your mail account (see SMTP Error 451 below).
But I know some antispam systems get abused to return 4xx even there is
neither temporary system problem nor server busy. They just doubt this
is suspicious message and return 4xx codes.
regards.
