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The JavaMail API is an optional package (standard extension) for reading, composing, and sending electronic messages. You use the package to create Mail User Agent (MUA) type programs, similar to Eudora, Pine, and Microsoft Outlook. Its main purpose is not for transporting, delivering, and forwarding messages like sendmail or other Mail Transfer Agent (MTA) type programs. In other words, users interact with MUA-type programs to read and write emails. MUAs rely on MTAs to handle the actual delivery.