i'm so screwed... the other night, my new-ish HP died. my old HP can do web browsing, but not MMOs, or zoom chat, things i was dependent on with social distancing enforced. i am very stressed out, not being able to do those, and barely able to work on the things that i need. i had Catalysts and Collections mailed between alts i am most likely going to lose, as it will take a miracle to get a new pc before mail deletes them. @ FK 200, or anyone who would pass a note to him, if anything they had sent to BatOracle 00, if they would just keep them or keep resending them, until i can play again, please. this could not have happened at a worse time.
The mail won't ever delete your stuff, after 60 days everything will stay in a limbo and the day you log in that stuff will be automatically sent back to the sender.
In your case, where you are sending items from one of your characters to another of your characters, if it gets auto returned-to-sender and then the sender also doesn't accept it in the amount of time before it expires, then all of the attachments auto-populate into the character's inventory. If you do not have enough space, they go into overflow and you must do inventory management before you are allowed to pick up any further drops. Same thing with stuff that expires that you posted on the broker. If you don't pick it up before the mail expires, it can't return-to-sender it back to the broker, so it just auto-populates into your inventory and overflow.