To ensure uninterrupted SMTP access and delivery?We have become more aggressive in our acceptance of SMTP connections and deny connections by IP address ( IP class )when these connections do not conform to Internet standard practices. ( lack of MX record or no Reverse DNS ) To ensure uninterrupted access to deliver of your mail to Accounts on our users, you must ensure that your email address lists are well maintained. If you are conforming to these standards, then these policies should not affect you.
If you consistently see 451 or 421 SMTP error codes, as well as rejection notices, you should review your email practices and policies, especially the following:
If you conform to the above practices and are still seeing delivery problems, please contact us so that we can help you diagnose your problem.
Remove email addresses that bounce. Bounces (also known as "non-delivery notices") are an indication that the mail could not be delivered because the user does not exist, no longer exists, or is otherwise unable to accept your email. List managers should remove addresses that generate bounces.
A particularly popular technique for managing bounces is to use VERP to identify the recipient address that has failed.
- Pay attention to the responses from our SMTP servers. The SMTP protocol defines response codes that tell your server what to do next.
In particular, our server will send 500 SMTP response codes to indicate problems that you need to investigate. For example, if an email is sent to an invalid recipient, our servers will respond with a 500 range SMTP code, indicating a permanent error.
Permanent errors should not be immediately retried. Many companies following best email list practices treat email addresses that have received a 500 range SMTP codes differently from other addresses. For instance, they may place these addresses into a special queue that tests for continued bounces after longer and longer periods of time.
This helps them maximize delivery to email addresses that do exist, minimize wasted bandwidth costs, and avoid behavior that may be seen as abusive by the recieving system. Failure to follow this practice will get your IP classes blocked.
- Don't send unsolicited email. Make sure that all email addresses are confirmed with an opt-in process that ensures the recipient wants to receive your mail. Obtaining permission from a third party to send an email does not ensure the email is solicited.
Probably the best way to confirm an email addresses before adding them to a mailing list is by using closed-loop confirmation (sometimes refered to as "full confirmation," "full verification," "confirmed voluntary subscription," or "double opt-in"). In this process, after you receive a subscription request, you send a confirmation email to that address which requires some affirmative action before that email address is added to the mailing list.
Since only the true owner of that email address can respond, you will know that the true owner has truly intended to subscribe and that the address is valid.
- Provide an easy method of unsubscribing from your list in each mail you send.
- Ensure that your mail servers are not open relays, and that your servers attempt to detect and deny connections to open proxies.
At a minimum, your SMTP servers should identify the originating IP addresses that of the email and indicate this in the email headers to help you diagnose spam problems. There are a variety of open relay testers available.
