[ranz]

Yahoo have an antispam mechanism which annoys most forum software emailing mechanisms. I recently contacted Yahoo Support about this and this was part of their email response:

If you are seeing a 421 error code in your SMTP logs indicating that the messages you are trying to send are "temporarily deferred due to user complaints," this means that we have observed unusual traffic patterns from your IP address and have been getting considerable complaints from our users regarding emails from your server.

Please note that this is not a permanent error; your system may automatically re-try after a while. We encourage you to try re-sending to our emails approximately 4 hours after you encounter this error. If, however, you are seeing this same error consistently over a 48-hour period, we encourage you to provide us with more information so that we can help diagnose your problem.

For bulk mail senders, please visit the URL below to review our best practice recommendations and request assistance.

http://help.yahoo.com/l/us/yahoo/mai...ster/bulk.html

If your mail server does not primarily send bulk mailings, please reply to this email and indicate the mail streams that are being sent from your email server(s), e.g., personal/corporate emails, transactional mailings, mailing list postings, newsletters.

It was a bit of a pain with a few back and forth emails - but I did actually reach a "human" at Yahoo and it was eventually sorted. We need yahoo to allow our email through as there are thousands of users on our forum which have yahoo email accounts.

I hope this information helps other vbulletin users.