Since the change of the mail system (or rather 30 days after), I cannot get any mail from other players (PC EU). This is a different bug as the one discussed here:
https://forums.elderscrollsonline.com/en/discussion/comment/7211418 , but it might have the same reason.
Every player who wants to contact me gets the error message that my mailbox is full. At first this didn't bother me since other players often said to me that I should clean my mailbox. My mailbox was constantly full at about 60-70 mails, some of them counted to the maximum (which should be 60, right?), some of them didn't. I usually kept a "buffer" of about 10 slots free (basically for my hirelings).
After the announcement of the new system I didn't bother to delete those old mails manually. I didn't care either, because most of them were personal notes or "trophies" which I saved before (if necessary).
After the purge I have ~20 mails which should be waaay below the maximum, still I can't get mails from other players. Funny thing: I
can still receive my hirelings' mail, system mails (daily rewards, expired sales and so on), COD and "return to sender" mails and mails sent via add-ons that contact all guild members (!).
This bug reminds me of the recently fixed (i really hope it
was fixed) bug concerning too much or too few skill points. The system seems to not check if the the
actual values are the same as they
should be! So, whenever ZOS decides: "Let's give (or take off of) players X of anything (skills, mails, probably more...)", there won't be any checks whether it is consistant or not!