I want to create an application that gets all e-mails from an e-mail account using imap. When I first run the application I get all mails, than if I run it again I want to mark the messages that was read before so I can receive only new messages.
I found that Message Object contains Flags(System Flags and User defined flags), but I can't manage to set one user defined flag.
It is possible to mark the messages received by my application on the e-mail account, or I have to retain all message ids and every time when I get messages from imap I have to compare their id with retained ids and get only the messages that has different ids?
Some IMAP servers don't permit you to set user-defined flags. Most do, however. Via JavaMail, you'd do the following:
Flags flags = new Flags("fetched");
message.setFlags(flags, true);
Those flags aren't permanent, however -- another IMAP client could clear them just as easily as you set them. (Though they probably won't.)
Another option is to track the UIDs of the messages you've seen. You can get them via ImapFolder.getUID(Message). It's more straightforward than tracking Message-ID headers, which are much more costly to fetch and, since they're strings, occupy more memory in your app.
Yet another option is to use POP and track UIDLs.