host wbeout.secureserver.net[220.127.116.11] said: 552
User has exceeded its 24-hour sending limit. Messages to 6868 recipients
out of 1500 allowed have been sent. (in reply to end of DATA command)
This isn't a terribly clear message, it looks very much is if there is meant to be a username after "User". My service provider has agreed that it's not a problem with my Zimbra installation sending too many messages, but won't investigate further because they can't reproduce the problem using their own system. I have changed all the passwords of course but it anyway doesn't seem likely to be a result of someone else impersonating me to send spam, as then all e-mail would presumably be blocked not just replies.
Has anyone else had this problem and found a work-around, by suppressing SMTP headers or similar?