I'll probably try turning it back on in a few days. I wanted to make sure that the email headers fix I put in was working 100% before I turned back on the auto-unsubscribing. (So far, no issues)
Below are the rough steps that trigger an auto-unsubscribe. If any step fails, no action is taken, just the bounce email is forwarded to my personal account to double check.
* Hosted email address receives an 'undeliverable' email response message into the inbox.
* Inside that undeliverable email body, the list server then attempts to parse out the original recipient and status error code that caused the bounce (yay regex!)
* If either can't be found, a 'notes' field is populated saying the error as well as to take a closer look at the bounce message and see if manual action is needed.
* If the failure error code equals any of the following, an unsubscribe gets triggered:
UNDELIVERABLE_EMAIL_ABORTED => "5.0.0",
UNDELIVERABLE_EMAIL_ACCOUNT_NOT_FOUND => "5.1.1",
UNDELIVERABLE_EMAIL_DOMAIN_NOT_FOUND => "5.1.2",
UNDELIVERABLE_EMAIL_ACCOUNT_DISABLED => "5.2.1",
UNDELIVERABLE_EMAIL_SENDING_DENIED => "5.7.0",
UNDELIVERABLE_EMAIL_POSSIBLE_SPAM => "5.7.1",
In all of the cases above, the email will get forwarded to my personal inbox. What steps were, or weren't, taken are populated in a 'notes' field at the top of the forwarded email.
When the headers were messed up, the test email I sent myself that caused me to get unsubscribed returned error code 5.7.1 which I guess makes sense because the message format was all messed up.
I was sort of on the fence with implementing this plan because of how annoying false positives can be for the end user. I only ended up doing it because of how insanely strict email hosts are about spam prevention (well, most at least). It's bad enough that if a bunch of people mark your messages as spam, it can cause a total blacklisting of your email address from sending mail out to other people in the future.
That's why I make sure to have the url of the site as well as an obvious unsubscribe link in all messages sent. I also make sure that my DKIM, DMARC, and SPF are all valid and legit. So far things have been pretty good since I've moved to the hosted email (knock on wood) but I do try to stay on top of any bounces which could hurt my email domain score and screw up the daily subscription emails that go out.
My guess is that strictness is why groups.io also has their auto
unsubscribe feature. It's just not worth chancing it by continuing to send to an address that bounced your email to it.