The "recent" addresses are extracted from actual messages stored on the device, every time, there is no separate storage.
As older messages are trimmed from the device's storage, the addresses in those messages will disappear too -- unless there are other, more recent, messages with same addresses.
If you need some addresses / emails for long term use, I recommend saving them in system Contacts (People), by tapping the sender's image (or color chip) in message view mode.