SMTP error from remote mailer after RCPT TO:<billing-ee@ryzom.com>:
host clarity.jolt.co.uk [195.149.21.11]: 553 sorry, your envelope sender is in my badmailfrom list (#5.7.1)
This happens when the server your email is being sent from has been blacklisted. To get around this situation, use a different email address to send your message. If you don't have another email address to use, you might want to try a free web based email solution such as offered by Yahoo or Google GMail.
*note to moderator: feel free to edit this if necessary.
Hope you don't mind me writing a separate thread here. Since I've seen this come up a few times recently, I thought it might make a good separate note.