Bouncing email and disabled addresses

In this post I will discuss a problem that plagues email groups: bouncing messages. I will start by explaining why email bounces, and what does about bouncing email. I conclude by providing some suggestions about what you can do about bouncing email, and what our plans are.

Why email bounces

When an email message cannot be delivered one of two things can happen. First, the message can be discarded. This is often done when the message looks particularly nefarious. Second, the system that sent the message can be told that the email was not delivered, in what is known as a bounce. In our experience here at bounces usually occur because of errors, full email in-boxes, and spam filters.

Sometimes an email message cannot reach its destination because there is an error somewhere along the way. Some of these errors may be with the network, or someone could have kicked the power-cord out from the mail-server, for example. These issues normally are fixed within a few hours.

Sometimes the email server will refuse to deliver a message because the recipient has a full in-box, and bounces the message back to us. Yes, in this day of near unlimited storage with the likes of GMail and people still run out of space. A full in-box is usually fixed once the owner is made aware of the problem — normally when they return from holiday.

Less common, but not unheard of, is an email address disappearing entirely. This typically happens when someone uses their work email address with a group, and changes jobs.

Email messages can also be bounced if the email looks like spam. Email that is bounced as spam seems to occupy the space where the message may be spam, or may be legitimate. (If a system is sure the message is spam then the email is usually discarded.) Email from your group is more likely to be seen as spam if the group members mark the messages as spam, rather than leaving the group — which happens a lot.

What does about bouncing email

At we do three things when we receive a bounce message.

  1. We track the email accounts that generated the bounce.
  2. We notify the owner of the email account that it is bouncing. (However, we can only do that if the person has more than one email account; more on that later.)
  3. We disable an email address if messages repeatedly bounce.

I will expand on the last point. If sent email to bouncing addresses then we would be classified as a spam source and all messages from all groups would be blocked. However, many delivery problems are intermittent, and disabling addresses whenever received a bounce would cause undue disruption to the people that use Our experience has shown that email accounts that bounce on five separate days within a 60 day window have serious issues and should be disabled.

Email addresses are disabled by setting them to unverified. This means that the owner of the address has to sign in, visit his or her profile, go the Change email settings page and send an email-address verification message. (If the owner only has one address then resetting a password will also verify an email address.)

What to do about bouncing email

If someone is has a bouncing address, or is missing out on email email then it is always good to enter a conversation to try and figure out what the underlying problem is. Include us in the conversation by sending an email to We cannot, and will not, “just” send people email as that will stop everyone from getting email.

People will automatically be contacted if they have multiple addresses. At we strongly encourage people to add all their email addresses to their profile. (Go to the Change email settings page to add an address.) This can help when one account stops working, or when someone needs to reset a password from home when they normally access the group from work.

Often the problem is the messages are being classified as spam. Add the email address of the group as a contact to help messages get through. In addition, switching to digest mode (click on the gear-icon at the top right of the Group page) can help for a couple of reasons.

  • Digests look less like spam, especially when group members tend to post many short messages.
  • People get less email with digests, at most once a day, which makes your group look less like a spam source.

The final thing you can do is invite people to join groups, rather than adding them. By inviting someone you ensure their email address works right from the start. In addition the person is only counted towards the maximum number of members for your site after he or she has accepted the invitation to join the group, making the person “free” while we sort out the delivery issues. In addition, people who have been invited are more likely to engage with the group, and will be more able to go onto digest mode, or leave the group, on their own volition.

Our plans for bouncing

At we endeavour to deliver all the posts that we can.

  • We continue to monitor the reports of spam from the large providers of email accounts, ensuring that we are only sending email to those that want to receive it.
  • We are continuing to ensure that we are seen as a good source of email by implement protocols such as DKIM and DMARC, as well as dealing with the subtle corners of IPv6 and TLS compatibility.
  • Finally, we are planning to improve how bounces are handled by the open source GroupServer system that powers

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