We have a lot of users of our product who sign up with team email aliases. Some higher-ups at big enterprises are on multiple distribution lists and so when we send out an email, they get multiple copies. I've been asked to investigate if there is any way to automatically identify these distribution lists so we can not subscribe them to emails. I can't think of any way (they're not going to follow an easy structure like marketing@ or sales@, we're talking about big orgs with lots of divisions). Any ideas, Marketing Nation?
Nope, or not in any widely useful way.
By definition, a distribution list will transparently route to each end user's mailbox. The only way you could possibly know the difference is if you get an OoO message from a different end-user address and are able to compare this with the recipient's original data, which you'd have to encode in the From: address.
Anyway, why wouldn't you want to subscribe them? You can't just substitute the individual email address for the list address (that's not legal) so you'd end up not being able to market to them at all. If they signed up via the distro list, that was maybe a bad move on their part, but you aren't doing anything wrong or something you can feasibly correct.