Deferrals Page

Deferrals

The deferrals page is the third page of the MTA policy wizard. This is where you can configure how long to wait after you've received a deferral notice or 'backoff' from the mailbox provider domain.

A backoff or deferral is an SMTP reply asking you to pause sending for awhile before trying again. Historically referred to as gray-listing, deferral codes are typically tied to your sender reputation with a mailbox provider such as gmail, yahoo, icloud, etc.

The universal retry time will be the default timeout applied to a SMTP backoff request, you can customize the amount of time to wait based on the content of the SMTP reply further down the page.

You can enter multiple time periods separated by commas to automatically increase the wait each time a consecutive delivery attempt is deferred without at least 1 successful delivery in-between.

You can implement a longer pause based on the total amount of email successfully delivered over a prior time period, rather than only if at least one email was accepted on the last delivery attempt. This may give you a more accurate/granular ability to throttle your email based on your current reputation with the receiver.

Example

Special deferral message retry time

Sometimes you may want to pause for a custom wait time to respect the preferences of the receiving mailbox provider based on the information in their SMTP reply.

For instance, you may see backoff requests in your ip delivery report deferral messages such as "too many messages sent this hour", in which case you may want to make a special deferral message retry for 1 hour or 61 minutes for that SMTP reply.

This may improve your sending reputation with the mailbox provider, but as with everything in email YMMV and mostly you can only employ best practices, send wanted mail, and hope for the best.

In this example, Comcast postmaster support tells a sender how long to pause based on the content of the SMTP reply the postmaster sees the sender receiving in Comcast's mail server logs.

Based on this information we would create the following special deferral message retry time.

But then sometimes, we don't want to wait.....

SMTP replies can be wrong.

SMTP is noisy

Compared to most internet-wide communication protocols, SMTP is often implemented in non-standard and individualized ways, and errors are also common. Whenever you receive an SMTP reply coded as a deferral you're going to pause for the universal deferral retry time, which means mail stops being delivered for that time period, which means you only want to stop sending if that's really what the receiving host is telling you to do.

Enter Transient Deferrals

By specifying an erroneous or irrelevant deferral coded SMTP reply as transient, you'll ignore the response and continue to deliver email as normal without imposing a pause.

Only recommended if you know what you're doing.