Excessive mail suppression.
I agree that this is borked. I started a new character the other day with 4 of my guild mates. We decided to play/level up at the same time and chose the Norn area for that since 3 of us had Norns and the other two were Asura.
I attempted to send 5 silver to three of the newer members for them to be able to purchase consumable harvesting equipment and a few salvaging kits along with some other miscellaneous items they felt they needed before the were able to get to their bank.
The first two mails went just fine but the third did not with the same “excessive mail” notation. Oddly, about a half an hour or so later that third person I sent a piece of equipment to and it went through along with the original 5 silver I intended to send in the first place.
If these folks are not only in my guild, but also on my friend’s list, why on earth are we blocked? Makes no sense what-so-ever.