HELP ! Too many login attempts

[wxPhil]

AMS is failing to send any emails, logging
"The mail server does not support authentication code 334. You may want to change the SmtpAuthentication value. 504 AUTH disabled due to too many login failures."
I've tried re-booting, stopping/re-starting the service - nothing - what can I do?

[wxPhil]

After teh n-th re-start it seems to have cleared....