1. Mail Services

2. A Mail Server’s Function
A mail server has basically 4 Functions
Accept Mail (From other servers)
Send Mail (To a remote server)
Accept Mail (From one user to be sent out to another server)
Send mail (To end user)

3. A sample Message POP or IMAP Outgoing mail server SMTP
Incoming mail server
SMTP
User B
User A

4. The Messaging process
When a message is sent to a mail server it uses SMTP (Simple Mail Transfer Protocol) to send the message.
SMTP uses port 25 on the accepting mail server.
When the message arrives at the destination server it is then downloaded by a mail client using either POP3 or IMAP protocols

5. POP Post Office Protocol
When you read your mail, all of it is immediately downloaded to your computer and no longer maintained on the server.

6. IMAP Internet Message Access Protocol
protocol in which is received and held for you by your Internet server.
Your client can view just the heading and the sender of the letter and then decide whether to download the mail

7. Features of IMAP
You can also create and manipulate folders or mailboxes on the server, delete messages, or search for certain parts or an entire note.
IMAP requires continual access to the server during the time that you are working with your mail.

8. IMAP Vs POP IMAP can be thought of as a remote file server.
POP can be thought of as a "store-and-forward" service.

9. Common Email Port Addresses
110 pop3
25 smtp
143 imap

10. Relaying Messages
Relaying is the process of sending or forwarding the message.
Most mail servers will restrict where the forward messages from this is to reduce spamming.
This is accomplished by setting a number of rules stating who is authorized and who isn’t.

11. What makes a user authorized?
IP address
Login/password
The sender’s domain
The sender’s address
The reply to address matches the sender’s address
The receiver's address/domain
Outgoing Mail Server
BLOCKED
Authorized user
Unauthorized user

12. Different Unix Mail Servers
Sendmail
Qmail
POSTFIX
SMAIL
EXIM
MMDF
ZMAILER

13. Other Mail Servers Exchange - Microsoft GroupWise - Novell
Lotus notes – IBM

14. The SMTP Protocol HELO hotmail.com bobo@bobo.com
Greet the mail server. Used once per session - at the beginning of the session.

15. The SMTP Protocol MAIL FROM: <from>
Announce who the sender is. Used once per mail, before specifying any recipients for each mail, or after a RSET.

16. The SMTP Protocol RCPT TO: <rcpt>
Announce who the mail is to. Multiple recipients are allowed, each must have its own RCPT TO: entered immediately after a MAIL FROM:

17. The SMTP Protocol
DATA
Starts mail entry mode. Everything entered on the lines following DATA is treated as the body of the message and is sent to the recipients. The DATA terminates with a . (period) on a line by itself. A mail may be queued or sent immediately when the . is entered. It cannot however be reset at this stage.

18. The SMTP Protocol RSET QUIT
Reset the state of the current transaction. The MAIL FROM: and RCPT TO: for the current transaction are cleared.
QUIT

19. The SMTP Protocol DATA From: me@mymachine To: bobo@bobo.com
Subject: A test message
This is gonna be like a small info bulletin on how

20. A sample SMTP Session homer:~$ telnet mx06.hotmail.com 25
Trying
Connected to mx06.hotmail.com.
Escape character is '^]'.
220-HotMail (NO UCE) ESMTP server ready at Thu, 14 Feb :52:
220 ESMTP spoken here

21. A sample SMTP Session helo fred@fred.com mail from: bigelow@rcc.on.ca
250 Requested mail action okay, completed
mail from:
rcpt to:
data
354 Start mail input; end with <CRLF>.<CRLF>

22. A sample SMTP Session con’t
From:
To:
Subject: Hello
This is a test .
250 Requested mail action okay, completed
quit

23. The POP Protocol telnet popserver.ca 110
+OK QPOP (version 2.53) at popserver.com starting.
USER username
+OK Password required for hacker.
Pass password

24. POP Protocol LIST _shows messages RETR – Downloads Messages
DELE – Deletes a Message