[messages] [Module General Discussion] What are bounces ?

uckelman uckelman at nomic.net
Mon May 5 23:58:01 CEST 2014

Here's what went out a few minutes ago to list subscribers who were
automatically unsubscribed:


You're receiving this because vassalengine.org's mailing list which
bridges the VASSAL forum automatically unsubscribed you. We did not
unsubscribe you intentionally. Here's why this happened. It's a bit
technical, so bear with me.

1. Mailing lists resend mail, but typically preserve the From header
of the orignal message. E.g., if I send a message to
messages at vassalengine.org[1], it will have

  From: Joel Uckelman <uckelman at nomic.net>

as one of the headers, and when our mailing list sends that message
out to list subscribers, it will still have that header unchanged.
The important point here is that the domain in the From header---in
this case, nomic.net---is not the same as the domain where our mailing
list lives---vassalengine.org. This is completely normal, and is how
mailing lists have worked the entire time that mailing lists have

2. In April, Yahoo set its DMARC policy to "reject". DMARC is a way
for owners of domains to signal what should be done with mail that
fails SPF or DKIM tests and has a From address in the owner's domain.
Lots of major email providers check DMARC, but until recently, no
large email providers had set their policy to "reject".

3. If the previous two points made sense, you should now see the
problem: If someone with a Yahoo email address posts to our list, then
any email server which checks DMARC to which our mailing list sends that
message will bounce the message back to us. This means that Yahoo's
policy change causes some of you not to receive messages from people
with Yahoo addresses---and not just those of you with Yahoo addresses
yourself, but also those of you whose email providers also check DMARC
(such as GMail). 

4. Many mailing list managers, including our own, automatically
unsubscribe addresses after some number of bounces. This is why you
were unsubscribed: Your email provider bounced back to us messages
sent by users with Yahoo-hosted addresses.

5. This is crappy. The "solution" that a lot of mailing lists have
adopted is to boot anybody with a Yahoo address. Unfortunately, we can't
do that. The reason we can't do that is that our mailing list is bridged
to our forum. One consequence of this is that people who are not list
subscribers are constantly posting to the list via the forum, which is
after all the entire point of a list bridge. Lots of them have Yahoo
addresses, and we can't reasonably stop them from using the forum.

So, the upshot of all of this is: We have a problem that I'm unsure how
to address presently. I have two possible solutions in mind, but I'm
going to need a bit more time to determine which we should do. Don't
expect anything to be fixed before next week, but do expect that this
will be fixed.

In case you'd like to read a bit more about what Yahoo did, here are
a couple of links:

  http://www.pcworld.com/article/2141120/ ... icy-breaks[2]

[1] mailto:messages at vassalengine.org
[2] http://www.pcworld.com/article/2141120/yahoo-email-antispoofing-policy-breaks
[3] http://jl.ly/Email/yahoobomb.html
[4] https://www.virusbtn.com/blog/2014/04_15.xml

Read this topic online here:

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