Anyone is having issues to deliver emails to yahoo.com ? I´m getting lot of emails stuck in queue with 451 temporary rejected or 421 deferred message. Seems that yahoo implemented graylisting in their servers. I have mails stuck in queue for 8 hours, and at night they are released. I received a mail from yahoo telling me that this is normal. I would like to hear comments of this. This is the email that yahoo send me: Thank you for writing to Yahoo! Mail. We appreciate your report as your input helps us to identify ways to constantly maintain and improve our service. We apologize for any inconvenience this has caused you. If you notice any further difficulties when delivering to Yahoo! Mail accounts, after waiting a reasonable amount of time, please let us know by replying directly to this email. However please note the following: If you are receiving the error code "421 Message from x.x.x.x temporarily deferred" or "451 Message temporarily deferred - 4.16.50" in your SMTP logs, this indicates that the message you attempted to send was not accepted by Yahoo! Mail servers. It is not a permanent error; your system will automatically re-try later. If, after attempting to deliver to Yahoo! and receive the 4.16.50 error repeatedly and conform to the best sending practices outlined in the following page, we encourage you to apply for prioritized sending at the link below. Recommended Best Practices: http://help.yahoo.com/help/us/mail/defer/defer-01.html Prioritized Delivery (Please note that this form can also be used by senders whose mailings are being directed to the Bulk Folder): http://help.yahoo.com/l/us/yahoo/mail/yahoomail/postmaster/bulk.html If you are receiving a separate error than that above, please provide the text of any error messages you may have received. Also, providing the specific IP address of the mail server that experienced the delivery issue will help us to troubleshoot the issue more efficiently. For assistance with delivery issues to Yahoo! Mail, please visit: http://postmaster.yahoo.com/ We appreciate your patience while we work to improve and maintain our service. Thank you again for contacting Yahoo! Mail.