I know that I can only hold a maximum of 8 items in my mailbox in Pocket Frogs. Right now, I'm using it as kind of a pseudo-storage while I make more money to be able to afford to buy more habitats. The ingame Help section doesn't mention anything about there being a limit to how long you can keep items in your mailbox, but I want to make sure that there truly isn't such a limit.
I have a few frogs that I have found and that have been sent to me that I'm leaving in my mailbox because I don't currently have room for them. Is it safe to leave items there, or do I risk them being accidentally deleted if I let them linger for too long?