I have recently been working with javamail. Right now, I am trying to store all mails in a file. For such a thing, one would need a unique ID, so I assumend UID would fit best here. However, I noticed something odd: A mail in the "Inbox" Folder with the subject "Hello" has the UID 10. If I fetched the same message from the "All Messages" folder, I'd get the same Message(because I am in "All Messages") with the same content, but with a different UID. This isn't actually that much of a problem, however, is it possible that two completely different mails from different folders might have the same UID? In this case, I would have to overthink the way i store mails.
Thanks in advance.
The UIDs are not JavaMail UIDs, they're IMAP UIDs, defined by the IMAP RFC.
The UIDs are unique per-folder, based on the UIDVALIDITY value for the folder. There is no unique ID for the folder itself.
Depending on your needs, you might consider using the Message-ID for the message, although note that while it's very, very likely to be unique, there's no guarantee that it is unique, and there's no guarantee that it exists for every message.