I guess this dry definition is not what you've been looking for. And indeed, it doesn't say or mean much, not to me either. This "transmission of messages" could be anything. But don't let that intimidate or confuse you. Email is as simple and straight forward as letter writing.
Email and Postal Mail
To get a grasp of what email is it's best — the terminology indicates it — to think in equivalents of "traditional" postal mail.
- The email message - Instead of using a pen to write a letter on paper, you're using your keyboard to type an email message in an email program on your computer.
- Sending the email - When the email is finished and has been addressed to the recipient's email address, you don't put a stamp on it and post it but press the Send button in the email program. This makes the email message go on its journey.
- Email transport - Like postal services transport letters and parcel, email servers transmit email messages from sender to recipient. Usually, emails are not delivered to the recipient directly, though, but waiting at the "nearest" mail server to be picked up by them.
- Fetching new mail - If you've got new mail in your mailbox, you go and fetch it. Similarly, your email program can check for new email messages at your mail server and download them for you to read.
If email is so much like postal mail, why would you use it and not write a letter?