Sending Email and Bounce Handling Rules

While listening to Stack Overflow Podcast 83 I was happy to hear I was not the only one that found sending email complicated.

The act of sending mail is also incredibly complicated because spammers have abused the infrastructure for a decade. There are a few immune responses that are still effective, such as DKIM and Reverse PTR records. SenderID is another method, also based on DNS records, but it’s less well regarded. If you’re going to send email and you want it to arrive, you need to implement all this stuff!.

I agree with this completely and would like to add some additional information about bounce handling. So after you get your Feedback loop setup with all the major ISPs, don’t blow it and ruin your reputation! Get some good bounce handling rules put in place.

The at sign, required character of the e-mail address.

The at sign, required character of the e-mail address.

Bounce Handling Rules

Your server will be put on a IP blacklist if you don’t handle bounces correctly. After you send a bunch of email the job is not done. The methodology I use for bounce handling was adopted from ISIPP’s white paper Bounce Handling Process, Email Delivery Rejection, and Receiving System Policies. I’ve been very happy with the results. Below is a brief summary, without getting into too much detail.

Hard bounce Handling Policy:

  • Description: If a hard bounce, spam complaint, unsubscribe feedback, or user initiated block is received I consider the email address dead and remove it immediately from all mailing lists.
  • Frequency: I check for these types to be immediately removed every 15 minutes.
  • Example: A hard bounce is permanent, “user unknown” being one good example.

Soft Bounce Handling Policy:

  • Description: Email address will be considered dead if the following criteria are met.
  • At least three delivery rejections have occurred in the last 30 days,
  • and user has had no successful deliveries in the last 15 days.
  • In addition, the time between the most recent delivery rejection and the initial delivery rejection is greater than 15 days.
  • Frequency: It’s acceptable to handle these types of bounces once per day
  • Example: Most commonly, a soft bounce is a temporary condition, such as “mailbox full.

Other areas you need to understand before sending emails include unsubscribe compliance, Mime Type Specifications, and email headers.

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