Have just received "error code 421: sent too many messages", although I was only emailing a text to a group of 46 at the time. One tip I came across was to reduce the total number of sent messages - mine are currently around 12,000 - and see what happens. Worth trying? Does it work?
Solved! Go to Solution.
Anti Spam precaution?
see 421 Too Many Messages - fails to send emails from ... - BT Community