iPhone Reply to All
The Reply All command on an iPhone works differently than other email software. iPhone/iPad does not enable the Reply All option when the From and To lines in an email are the same address. (Your Mailing List emails often have the same address in both places.)
If the author of the message has DMARC turned on, then the Mailing List address is used in the From line, instead of the author's address.
In addition, there is a Mail-List.com option that always inserts the Mailing List address is in the From line.
To compensate for this issue, we change the To header be a slightly different email address. Since From and To are then different, iPhone/iPad will then show the Reply All button.