For unittests (as MariuszS says) you should not connect to a real system. Have a look at JavaMail Mock2 https://github.com/salyh/javamail-mock2 ,this is designed for doing unittests with JavaMail and does not need a real system.
Its primarily focused on IMAP/POP3 but SMTP Mock is also available.
Its available in maven central.
Features
- Support imap, imaps, pop3, pop3s, smtp, smtps
- Supported for POP3: cast to POP3Folder, Folder.getUID(Message msg)
- Supported for IMAP: cast to IMAPFolder, cast to UIDFolder, Subfolders, -Folder.getMessagesByUID(...), delete/rename folders, append messages
- Support for SMTP: Mock Transport.send()
Unsupported for the moment: IMAP extensions like IDLE, CONDSTORE, ... and casts to POP3Message/IMAPMessage, store listeners