Why am I getting two copies of emails I send to some lists?

In this excerpt from
Answercast #69, I look at reasons that could be causing Gmail to display
double messages from a list membership.

Double emails

Well, the cause is I think relatively simple.

It is certainly possible that you could be on that mailing list, on that
group, twice. That certainly is something that’s easy to check for. Make sure
that your email address is actually on that mailing list or on that group
exactly and only once.

Double emails in Gmail

More than likely though, I suspect something else. Now, I believe that you
are coming to me, yes, from a Gmail address. So, here’s what could potentially
be happening.

When you send an email using Gmail, it actually puts the sent mail into
your Sent mail folder; and it may also show up in your Inbox as a new mail.
That’s simply on the act of sending the message. You haven’t even received it
yet; it’s only been sent.

I see this periodically when I send things to various email lists. I don’t
know if it’s intentional, but the fact is, emails will sometimes show up in my
inbox if I’m replying to a group list when I hit Send.

Now, what then may happen is that the email gets sent, goes out to wherever
the mailing list is handled, and the mailing list then turns around and sends
it back to you – so it shows up in your inbox again. Now, in my experience,
Gmail is very good about reconciling those two. In other words, I don’t get two
copies; but exactly how it does that is unclear. The fact is that the copy that
you sent and the copy that you then receive (by virtue of being on the email
list) should be for all intents and purposes the same.

I won’t say that they’re identical because the headers will change. The
headers on the email that you sent out will not include all of the additional
headers that get placed in the normal processing of that email as it goes to
the mailing list and back to you.

So, that’s the only thing I can think of that’s happening. Somehow, there’s
enough of a difference that’s added by the email processing software (the
mailing list that you’re sending to) that allows Google to miss the fact that
what you just sent is in fact what you just received from the mailing list
you sent it to.

So, I hope that makes a little bit of sense. In other words, what you’re
seeing is your outgoing copy first and then later your incoming copy by virtue
of being on that mailing list.

Stop duplicate emails

What to do about it? Well, in my case, I’d be really tempted to simply live
with it. It’s easy enough to delete things.

If you feel strongly that this an annoyance you want to get rid of, I would
look into setting up an inbox rule using a filter in Gmail. That would allow
you to somehow identify the mail that’s going out and then automatically
delete it – so that the only one that’s left is the final copy as it was sent
to the entire mailing list.

That’s the best explanation I can come up with. It’s what it sounds like.
It’s what came to mind to me as you described what’s going on here. I don’t
really have a great solution for making it go away, but fortunately, aside from
a double message in your inbox that’s easy to delete, it’s relatively
benign.