[Mailman-Developers] images embedded in html: inline vs. attached

[ryan]

Hi,

I've tried searching the list archives, and posting to the mailman-users
list, but I can't seem to find an answer to my problem.  Hopefully someone
on this list can shed some light...

A quick background: At the non-profit museum where I work, we use Mailman
to inform our paying members (and other general members of the public who
signup to our lists)  about our current exhibitions and events.  We like
to use HTML formatted messages with in-body (inline?) images for this
purpose.  It looks nice, and conforms with the overall look of our website
and other publications in print.  I realize sending out bulk HTML mailings
is probably not the most typical use of Mailman, but it works great for
us, and allows people who don't want our emails to quickly remove
themselves without requiring our intervention.

Here's the problem: Today I sent out 2 test messages to a pre-configured
list.  For the two tests, the list had only 6 staff members subscribed.  
The message looked great, everyone saw the content with the image
correctly aligned in the body of the message, between the two blocks of
text where it belonged.

However, after I added the 6700+ actual email addresses to the SAME list,
and sent out the SAME email, the image was removed from the body of the
message and included as an attachment instead.  This essentially made our
pretty little email look like crap.  This behavior occurred on all the
computers of the 6 staff members where I had previously tested, plus on
additional accounts that I was able to confirm through phone calls, etc.

Again, the same list (same configuration), and the same email were used
for the successful test and the unsuccessful real mail-out.  I cannot
stress enough that these were the *exact* same emails, for both the test
with 6 users, and the later mailing with 6700+; the filesizes were the
exact same, and the HTML was unchanged.

So... my only theory is: at some cut-off point, Mailman decides that there
are two many users on a list to embed an image in every email.  Perhaps
because you thought it more efficient to store the image once and then
reference it as an attachment when each member is emailed?

Or could this be some behavior of my mailer daemon, Sendmail?

Any thoughts?

Thanks in advance,
Ryan