From official ESO support page:
"For COD mails, if the player you have sent an item to does not open the mail and take the item, the item will be returned to you after it expires in 30 days. When a COD mail is sent, the recipient has three days to accept the mail. After this time, the mail and item(s) is automatically returned."
So which one is it ? Is it 3 days after I sent the mail and it hasn't been accepted or 30 ? It says both, one right after the other. Very confusing.
As it stands I sent several c.o.d.s last weekend (so almost a week ago now) to a friend who no longer plays because I was running out of inventory space and wanted to store some items in my mailbox. The mails still haven't been returned to me.