CIT 470: Advanced Network and System Administration Slide #1

1. Mail Policies
2. Anatomy of a Mail Message
3. Components of an E-mail System
4. SMTP
5. IMAP & POP
6. E-mail Addresses
7. Aliases and Lists
CIT 470: Advanced Network and System Administration Slide #2

1. Privacy Policy
2. Namespaces
3. Reliability
4. Scaling
5. Security
CIT 470: Advanced Network and System Administration Slide #3

Personal Use Policy
– Personal v. commercial use.
– When may employee e-mail be read?
• By whom
• Under what circumstances
– Automatic monitoring
Retention Policy
– Legal requirements.
CIT 470: Advanced Network and System Administration Slide #4

Avoid first.last format addresses.
– There will be duplicates: John.Smith.
– Use middle initials?
– Append numbers?
Create unique organization-wide namespace.
– Use directory to lookup addresses.
CIT 470: Advanced Network and System Administration Slide #5

Customers expect same reliability as power.
– Failures generate many support calls.
Reliability measures
– Redundant servers.
– Backup MX hosts.
– RAID arrays.
– Multiple NICs, power supplies, processors, etc.
CIT 470: Advanced Network and System Administration Slide #6

Types of scability
– To address growth in avg messages/day.
– To address spikes in mail traffic.
Number of messages grows
– faster than linearly with number of users.
– with time, even if user base is constant.
– due to spam too.
Size of messages grows
– due to technology: more + larger attachments.
CIT 470: Advanced Network and System Administration Slide #7

Mail server as a target
– Complexity of mail leads to vulnerabilities.
– Mail is an asset attackers want to take.
E-mail as a conduit
– Brings viruses and trojans into organization.
– Leaks confidential information outward.
– ex (2005): Apple sues bloggers over releasing data about upcoming products.
E-mail relaying
– Open relays used by spammers and scammers.
Intercepting e-mail
CIT 470: Advanced Network and System Administration Slide #8

Blank
Body
Received: from mailfe2.nku.edu ([192.122.237.68]) by brahms.utoledo.edu (8.11.9) with ESMTP id k3CJCM for <him@utoledo.edu>; Wed, 12 Apr 2006 15:12:22 -
0400 (EDT)
Received: from mailfac1.nku.edu ([172.28.102.15]) by mailfe2.nku.edu with MS SMTPSVC(6.0.3790.211); Wed,
12 Apr 2006 15:15:18 -0400
Subject: Test
Date: Wed, 12 Apr 2006 15:15:18 -0400
Message-ID: <F01E4499C4EC5842A@mailfac1.hh.nku.edu>
From: “You" <you@nku.edu>
To: <him@utoledo.edu>
This is a test message.
CIT 470: Advanced Network and System Administration Slide #9

Header Format
– Header-name: Header-data
Common headers
– From:
– To:, CC:, Reply-To:
– Date:
– Message-ID:
– Subject:
Multiple headers
– Received: for each mail server handling message.
CIT 470: Advanced Network and System Administration Slide #10

• Separated from header by blank line.
• Contains 7-bit ASCII text by default.
• Any non-ASCII text must be encoded:
– uuencode
– MIME
CIT 470: Advanced Network and System Administration Slide #11

Multipurpose Internet Mail Extensions
– Text in non-ASCII character sets.
– Non-text attachments.
– Multi-part message bodies.
Identified by Content-Type: header.
– text/plain: regular e-mail
– text/html: HTML markup
– multipart/mixed: text/plain + attachments
– image/jpeg: JPEG image attachment
– Many other formats
CIT 470: Advanced Network and System Administration Slide #12

Binary to text encoding scheme
– Each character represents 6 bits.
– Uses 64 characters from 7-bit ASCII: A-Za-z0-9+=
Encodes in 3-byte chunks
3 bytes = 24 bits = 4 base-64 characters
M a n
77 97 110
010011|01 0110|0001 01|101110
19 22 5 46
T W F u
CIT 470: Advanced Network and System Administration Slide #13

MIME-version: 1.0
Content-type: multipart/mixed; boundary="frontier“
This is a multi-part message in MIME format.
--frontier
Content-type: text/plain
This is the body of the message.
--frontier
Content-type: application/octet-stream
Content-transfer-encoding: base64
PGh0bWw+CiAgPGhlYWQ+CiAgPC9oZWFkPgogIDxib2R5PgogICA gPHA+VGhpcyBpcyB0aGUg
Ym9keSBvZiB0aGUgbWVzc2FnZS48L3A+CiAgPC9ib2R5Pgo8L2h0 bWw+Cg==
--frontier--
CIT 470: Advanced Network and System Administration Slide #14

Headers aren’t the full story
– Recipient isn’t necessarily on To: or CC:
– Sender isn’t necessarily given on From: header.
Envelope specifies sender/receiver
– Specified via SMTP commands.
– Envelope recipient used for BCC:
– Envelope recipient used by mail lists.
– Envelope facilities used by spammers too.
CIT 470: Advanced Network and System Administration Slide #15

UA
Eudora
DA mail.local
Msg
Store
UA
Outlook
TA
Sendmail
TA
Sendmail
UA mutt
UA mutt
AA imapd
CIT 470: Advanced Network and System Administration Slide #16

• Mail Transport Agents
– Receive mail from MUAs.
– Route mail across internet.
• MTA Protocol: SMTP
• MTA Examples
– sendmail
– postfix
– qmail
CIT 470: Advanced Network and System Administration Slide #17

220 brahms.nku.edu ESMTP Sendmail 8.13.3; Wed, 12 Apr 2006 helo mydomain.com
250 brahms.nku.edu Hello mydomain.com, pleased to meet you mail from: me@mydomain.com
250 2.1.0 me@mydomain.com... Sender ok rcpt to: friend@nku.edu
250 2.1.5 friend@nku.edu... Recipient ok data
354 Enter mail, end with "." on a line by itself
Subject: Test
From: me@mydomain.com
To: friend@nku.edu
This is a test.
.
250 2.0.0 k3GIcr001606 Message accepted for delivery quit
221 2.0.0 brahms.nku.edu closing connection
CIT 470: Advanced Network and System Administration Slide #18

HELO hostname
EHLO hostname
MAIL FROM: addr
RCPT TO: addr
VRFY addr
EXPN addr
DATA
QUIT
RSET
HELP
CIT 470: Advanced Network and System Administration Slide #19

• Communication
– Receives data from MDA (mail.local, procmail)
– Provides data to MAA (IMAP, POP, NFS, web)
• Types of stores
– Files (all messages for a user in one file)
– Directories (directory per user)
– Databases
CIT 470: Advanced Network and System Administration Slide #20

• Older systems directly accessed mail files.
• Modern systems use network
– POP: Post Office Protocol
• Simple download protocol for offline reading.
– IMAP: Internet Mail Access Protocol
• Online and offline modes of reading.
• Partial message fetch (headers, attachments, etc.)
• Message state stored on server, not client.
• Multiple mailbox and multiple client support.
CIT 470: Advanced Network and System Administration Slide #21

• IMAP Servers
– Cyrus
– UW
• IMAP Features
– Message store types
– Authentication
– Security (SSL)
CIT 470: Advanced Network and System Administration Slide #22

• Text clients
– mail
– mutt
– pine
• GUI clients
– Eudora
– Mozilla Thunderbird
– MS Outlook
• Web clients
– Run on remote web server.
CIT 470: Advanced Network and System Administration Slide #23

• Relative Addresses
– mcvax!uunet!ucbvax!hao!boulder!air!evi
• Absolute Addresses
– user@domain
• MX Records
– Mail clients use MX records, not A records.
– Lowest preference # = highest priority.
– Permits failover if server down.
CIT 470: Advanced Network and System Administration Slide #24

• Allow mail to be rerouted.
– Sysadmin: files (/etc/mail/aliases), local db, NIS, LDAP
– Personal: ~/.forward
• Alias destinations
– Local: address
– Remote: address@domain
– File: :include:pathname
– Program: |pathname
• Required aliases
– postmaster, abuse, root
CIT 470: Advanced Network and System Administration Slide #25

Mailing List Aliases mylist: :include:/etc/mail/include/mylist owner-mylist: mylist-request mylist-request: me owner-owner: postmaster
Purpose owner : Messages appear to be from owner. Receives bounces, list management mail.
request : Indirection ensures owner’s real address doesn’t appear on Return-Path.
owner-owner : Receives errors from messages destined for owner-* aliases.
CIT 470: Advanced Network and System Administration Slide #26

• Automate list management.
– E-mail interface.
– Web interface.
• Packages
– Mailman
– Majordomo
– Listserv
• List Archiving
– Mailman
– MHonArc
CIT 470: Advanced Network and System Administration Slide #27

1.
Bryan Cosales with Eric Allman, Sendmail, 3 rd edition , O’Reilly,
2002.
2.
David H. Crocker, RFC 822: STANDARD FOR THE FORMAT OF
ARPA INTERNET TEXT MESSAGES, http://www.ietf.org/rfc/rfc0822.txt
, 1982.
3.
Aeleen Frisch , Essential System Administration, 3 rd edition , O’Reilly,
2002.
4.
MIME, http://en.wikipedia.org/wiki/MIME
5.
Evi Nemeth et al, UNIX System Administration Handbook, 3 rd edition , Prentice Hall, 2001.
6.
Thomas A. Limoncelli and Christine Hogan, The Practice of System and Network Administration , Addison-Wesley, 2002.
7.
RedHat, Red Hat Enterprise Linux 4 System Administration Guide , http://www.redhat.com/docs/manuals/enterprise/RHEL-4-
Manual/sysadmin-guide/ , 2005.
8.
Alan Schwartz, Managing Mailing Lists , O’Reilly, 1998.
CIT 470: Advanced Network and System Administration Slide #28