The growing concerns surrounding spam and harmful computer viruses have caused many mail servers to blacklist all inbound email sent from suspicious domains and servers. As a result, users can no longer accept messages routed through a potentially dangerous server.

While this feature may reduce or even eliminate spam from a particular domain, it can also create a communication barrier within your business. For example, it could result in delayed email messages or undelivered email messages. In fact, many SmarterMail users have received the following delivery error message when sending email to Yahoo!:

If you are seeing the error code “421 Message received from x.x.x.x temporarily deferred” or “451 Message temporarily deferred” in your SMTP logs, this indicates that the message you attempted to send was not accepted at Yahoo!. It is not a permanent error; your system will automatically re-try later.

If you are seeing this same error consistently over an extended period of time, and you feel that your policies and practices comply with our guidelines (described below), we would encourage you to contact us with detailed information so that we can help diagnose your problem.

For bulk mailers please visit ( http://help.yahoo.com/l/us/yahoo/mail/postmaster/basics/postmaster-02.html ) to review our best practice recommendations and, if appropriate, request assistance.

If your mail server does not primarily send bulk mailings (e.g, you run a personal, corporate, educational, or ISP mail server), please visit ( http://help.yahoo.com/l/us/yahoo/mail/postmaster/defer.html ).

If you are not the administrator of the mail server in question, please contact the administrator directly with the error message you are receiving.

-- From Yahoo! Mail Help (http://help.yahoo.com/l/us/yahoo/mail/postmaster/errors/postmaster-04.html)

Yahoo!’s introduction of DomainKeysIM (DKIM), which combines DomainKeys and Identified Internet Mail (IIM), requires additional security measures to ensure safe email messaging. To prevent being "deferred" by Yahoo!, the following configuration changes for SmarterMail are recommended:

1. Verify that a reverse DNS record is in place for all IPs that SmarterMail uses for outbound SMTP connections.
2. Verify that an SPF record is in place for all hosted domains.
3. Verify that DomainKeys/DKIM signing is enabled for your domains. (Versions 15.x and later no longer support DomainKey signing as that method for mail signing has become obsolete.)
4. Use an outbound gateway with SpamAssassin and outbound filtering.

If this configuration does not resolve your deferment issue, you must become whitelisted by Yahoo! to ensure continued email delivery. To begin, you will need to fill out the appropriate form based on your email needs. If you send bulk email out on a regular basis, you will need to complete the Yahoo! Mail Bulk Sender Form. Alternatively, if you do not send out bulk mailings, you will need to complete the Yahoo! Mail Delivery Issues Form. Yahoo! may report that there are too many domains assigned to the same IP (Shared IP); however, with repeated requests, you will still become whitelisted.