How do I uniquely identify a Java Mail Message using IMAP?

Question

IMAP Message in Java Mail is identified by it's relative position number which starts from 1.

refer, http://docs.oracle.com/javaee/1.4/api/javax/mail/Message.html#getMessageNumber()

Message number is a temporary details.

Is there a way to permanently uniquely identify a mail/message which accessing a mailbox via IMAP using Java Mail API which holds true across sessions ?

Answer 1

Look at the UIDFolder interface, which exposes the IMAP UID capability.

Answer 2

You can get a unique identifier for a message using the following code as an example

Folder folder = imapStore.getFolder("INBOX"); // get reference for inbox folder
UIDFolder uf = (UIDFolder)folder; // cast folder to UIDFolder interface
folder.open(Folder.READ_ONLY); // open folder
Message messages[] = folder.getMessages(); // get all messages
Long messageId = uf.getUID(messages[0]); // get message Id of first message in the inbox

Answer 3

Adding this because I think this will help

If you want to loop over the messages and get uids the above code does not do got performance as you have to loop and get uid, easy way to get that with the messages is below

Folder emailFolder = store.getFolder("INBOX");
emailFolder.open(Folder.READ_ONLY);
UIDFolder uf = (UIDFolder)emailFolder;
Message messages[] = emailFolder.getMessages();
            
FetchProfile profile = new FetchProfile();
//profile.add(FetchProfile.Item.ENVELOPE);
profile.add(FetchProfile.Item.FLAGS);
//profile.add(FetchProfile.Item.CONTENT_INFO);
profile.add(UIDFolder.FetchProfileItem.UID);
emailFolder.fetch(messages, profile);

this will get the messages with the uid

after this if you loop and do uf.getUID(messages[i]); you will get the uid but this time it will be faster.