Question

Consider an employee using their computer to send and retrieve email at their workplace. Only Ethernet networks are used for physical connectivity, but the mail server is located on a separate network. The employee’s network and the mail server’s network are connected by a single router which also has a connection to the Internet via the workplace’s ISP.

Explain how the employees email client sends and receives emails using the email server, indicating any protocols involved and where any encapsulation/decapsulation occurs as data travels between the client, local mail server, and remote mail servers.

Answer 1

What Is IMAP?

IMAP(Internet Message Access Protocol) is the protocol used by the vast majority of consumer email accounts. With IMAP, emails are stored on an Internet server. When a user accesses their account, they’re connected to the external server, and data is transferred from the server to their local machine – which itself doesn’t actually receive any email messages.

One of the key advantages of IMAP – aside from remote access – is that it allows a single account to be operated and managed by multiple users, without the need for a complex workaround. It can also put a fair amount of strain on your mail server, if your business manages its own email service.

In order for IMAP to function, it requires one of two ports to be open:

• Port 143: The default IMAP port; this allows the protocol to listen for incoming requests to synchronize emails. Traffic through this port is unencrypted.
• Port 993: Used for IMAP over SSL.

What Is POP3?

Unlike IMAP, POP3 (Post Office Protocol 3) downloads messages from a mail service to a user’s local computer. This allows the user to not only receive emails on their own machine, but also to disconnect from the Internet and retain access to all of their messages. There are a number of advantages to this approach.

First and foremost, unless you’re opting to leave a copy of each email on the mail server, it clears up a significant amount of space by storing all files on the user’s local machine. This makes it much easier to back up one’s email messages, in addition to making search and organization far more efficient.

Unfortunately, POP3 isn’t without its weaknesses either. The protocol by default assumes that only a single user will be accessing a particular email account, meaning that you’ll need a workaround if you want multiple users on a single email. In addition, remote access can be something of a problem. Finally, the fact that most POP services delete downloaded emails from the server by default makes it incredibly difficult to synchronize an account to multiple machines.

POP3 requires one of the following two ports to be open:

• Port 110: For unencrypted POP3 access; this is the default listening/communications port.
• Port 995: Used for encrypted POP3 connections.

these are two protocols used over network for email communication

from this IMAP is widely used.

What Is SMTP?

Now, though there are two protocols associated with receiving emails, there’s really only one associated with sending them. SMTP(Simple Mail Transfer Protocol) is the gold standard for passing email messages from one mail server to another. Every email service uses some variation of this protocol.

There’s one more difference between SMTP and IMAP/POP3: unlike the latter two, it requires no authentication to function. Although modern SMTP applications restrict relaying, this nevertheless allows for a fair volume of spam to exist on the web; some tech-savvy criminals can even send emails using another’s account.

There are two ports you’ll need to be aware of for SMTP:

• Port 25: This is the default SMTP port. It is not encrypted.
• Port 465 / 587: The default port for using SMTP through SSL.

In addition, some hosts may offer a secondary port as an alternative to clients for whom port 25 is filtered.