I'm a junior Java developer and I'm training some basic things.

I've programmed an easy JakartaMail client to send an email. I've tested it's functionality through an online service: mailtrap.io

The email source code shows in the Message-ID that the email comes from my very computer Message-ID: <###CODES###.MYUSERNAME@MY_COMPUTER_NAME>

Has my LAN somehow ports open to connections? I understand that my program makes a call to the email server I'm using and sends the email information through it, how is my PC machine name involved in the sending.

CodePudding user response：

The Message-ID is generated by JavaMail/JakartaMail when you send the message. As it is running on your machine, it knows the host name, etc, and uses that to generate the message id. The Message-ID is intended to (preferably uniquely) identify a message, including the host name of the sender in that Message-ID makes it more likely to be unique.

And given your application runs on your machine, that is the machine that communicates with the mail server. However, it doesn't open any ports on your machine (other than the ephemeral port used for the TCP/IP connection to the mail server).