If someone wants to run a mailing list they should use a mailing list
management software that's designed for that purpose, instead of
trying to shoehorn something out of an ordinary E-mail client.
Totally agreed on that.
The lack of functionality that had been objected against mailing
list software is the ability for recipient X to determine if last
week's broadcast message had [or should have] been delivered also
to recipient Y. In this respect, ordinary mail gives a suboptimal
solution, as the "To" headers should match the list of recipients.
We have put in place restrictions and policies nicely forcing customers
into using mailing list management tools to do their broadcasts.
What do you mean by "nicely forcing"? Do you have semi-automated
procedures, step-by-step instructions, or similar guidance for
setting up mailing lists on your server?