We’re occasionally asked why someone who didn’t try to unsubscribe from a list would receive a message with a subject of “Verify your removal from the example.com listname mailing list”.

The most common cause of this is that person A sends a message to a “group discussion” list, and it’s received by another subscriber, person B, with the usual unsubscribe instructions at the bottom:

From: Person A
Subject: Tigers

I'm going to donate to the endangered tiger fund.
_________________________________________________________________
To unsubscribe or modify your subscription options, please visit:
http://lists.example.com/mailman/options/listname/PersonB%40example.net

That link is a private unsubscribe link for person B. However, occasionally person B replies to the entire list and includes the link in the reply, so that every list member sees a copy of person B’s personalized unsubscribe link.

For example, if Person B replies to the list and includes their private link in the reply, person C could see this:

From: Person B
Subject: Re: Tigers

I am, too!

On July 4, Person A wrote:
>I'm going to donate to the endangered tiger fund.
>
>_________________________________________________________________
>To unsubscribe or modify your subscription options, please visit:
>http://lists.example.com/mailman/options/listname/PersonB%40example.net

_________________________________________________________________
To unsubscribe or modify your subscription options, please visit:
http://lists.example.com/mailman/options/listname/PersonC%40example.org

Note that this contains the personalized unsubscribe links for both person B and person C, because person B accidentally sent his or her link to everyone. And if person C wants to unsubscribe, they may click on Person B’s first link instead of their own link.

Many mail programs remove the original message’s “signature” when you reply to a message, avoiding this problem. If the mail program doesn’t do that, person B should ideally remove it manually when he or she replies to a message, but it’s a hard thing to get into the habit of doing.

How do I permanently prevent this from happening to anyone?

If this is an ongoing problem and you want to completely stop it, you could remove the personalized link from each message and replace it with a generic one, since it doesn’t matter if someone sends the generic link back to the list. To do that:

• Login to your Mailman management page
• Click Non-digest options
• Scroll down to “Footer added to mail sent to non-digest list members”

It will look something like this:

To unsubscribe or modify your subscription options, please visit:
%(user_optionsurl)s

You could change that to:

To unsubscribe or modify your subscription options, please visit:
%(web_page_url)s/listinfo/%(list_name)s 

If you do that, the footer won’t be personalized — instead, it will take people to a page that requires them to manually type the email address they want to unsubscribe.

Doing this will solve the initial problem. But it will also make it slightly harder for people to unsubscribe. You should be prepared for some people to mistype their email address and then send you a message that the form “won't accept my address”; we see this fairly often when people are asked to type their email address.