Suppose Alice, with a Web-based e-mail account (such as Hotmail or gmail), sends a message to Bob, who accesses his mail from his mail server using POP3. Discuss how the message gets from Alice’s host to Bob’s host. Be sure to list the series of application-layer protocols that are used to move the message between the two hosts.

The process of sending an email from Alice to Bob involves several steps and a series of application-layer protocols. Here's a step-by-step breakdown:

1. Alice composes an email on her web-based email client (like Gmail or Hotmail). This is done using a web browser, which communicates with the web server hosting the email service using the HTTP (Hypertext Transfer Protocol) or HTTPS (HTTP Secure) protocols.

2. Once Alice hits 'send', the email is sent to her email service's SMTP (Simple Mail Transfer Protocol) server. SMTP is the standard protocol for sending emails across the Internet.

3. The SMTP server begins the process of routing the email to Bob's mail server. If the SMTP server doesn't know the location of Bob's server, it will use the DNS (Domain Name System) protocol to look up the mail server associated with Bob's email address.

4. Once the SMTP server knows where to send the email, it opens a communication channel to Bob's mail server, again using SMTP, and sends the email.

5. Bob's mail server receives the email and stores it. When Bob checks his email, his email client communicates with his mail server using the POP3 (Post Office Protocol version 3) protocol to download the email.

6. Once the email is downloaded via POP3, it's stored locally on Bob's device and he can read it using his email client.

So, the series of application-layer protocols used to move the message between Alice and Bob are HTTP/HTTPS, SMTP, DNS, and POP3.