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SMTP PROTOCOL CONFIGURATION AND MANAGEMENT

SMTP PROTOCOL CONFIGURATION AND MANAGEMENT. Chapter 8. OVERVIEW. SMTP and ESMTP DNS MX records Internet connectivity SMTP virtual servers and connectors Relaying and smart hosts SMTP security Global settings Domain nodes Per-user settings. HOW SMTP IMPLEMENTS A CONNECTION. Server.

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SMTP PROTOCOL CONFIGURATION AND MANAGEMENT

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  1. SMTP PROTOCOL CONFIGURATION AND MANAGEMENT Chapter 8

  2. OVERVIEW • SMTP and ESMTP • DNS MX records • Internet connectivity • SMTP virtual servers and connectors • Relaying and smart hosts • SMTP security • Global settings • Domain nodes • Per-user settings

  3. HOW SMTP IMPLEMENTS A CONNECTION Server Host Initiates a TCP connection Response 220 Response 250 Sends helo command Response 250 Identifies the sender using mail from: Response 250 Identifies the recipient using rcpt to: Indicates ready to send using data Response 354 Sends message Waits for quit Indicates end of session using quit Response 221

  4. HOW ESMTP IMPLEMENTS A CONNECTION • Host sends ehlo instead of helo • If server supports ESMTP it returns response 250 • If server does not support ESMTP it returns response 500 • ESMTP session very similar to SMTP session

  5. SMTP SYSTEM FOLDERS • Pickup • Queue • Badmail

  6. CONFIGURING MX RECORDS • Managing your own DNS: • Single namespace • Multiple namespaces • Internet service provider (ISP) manages your DNS: • Nonpersistent connection • Permanent connection

  7. CONFIGURING INTERNET CONNECTIVITY • Configuring SMTP virtual servers • Creating and configuring an SMTP Connector • Configuring an SMTP policy for a domain • Configuring per-user settings

  8. DEMONSTRATION: CREATING AND CONFIGURING AN ADDITIONAL SMTP VIRTUAL SERVER

  9. DEMONSTRATION: CREATING AN SMTP CONNECTOR

  10. DEMONSTRATION: CONFIGURING AN SMTP CONNECTOR • Limiting the scope • Configuring the credentials • Configuring to only receive e-mail • Configuring to only send e-mail • Configuring Internet message formats • Configuring message delivery parameters

  11. SMTP RELAYS • SMTP virtual server configured to use a smart host • SMTP virtual server forwards unresolved messages to a smart host • SMTP virtual server configured as a relay host

  12. SMTP RELAYS (CONT.) • SMTP virtual server configured to limit the servers that can relay e-mail messages • SMTP Connector configured to use a smart host • Configuring domains to which you want to relay messages

  13. SMTP VIRTUAL SERVER CONFIGURED TO USE A SMART HOST • Virtual servers forward all outbound mail to a smart host • Virtual server does not resolve the SMTP domain name • Entry and exit point for all Internet messages • Entry and exit point for messages to a foreign messaging system

  14. SMTP VIRTUAL SERVER CONFIGURED TO USE A SMART HOST (CONT.) • Helps manage Internet message traffic • Provides dial-up solutions • Clients do not need permanent connections to the Exchange server

  15. SMTP VIRTUAL SERVER FORWARDS UNRESOLVED MESSAGES TO A SMART HOST • Forward all unresolved SMTP messages from Exchange to a smart host • Other SMTP messaging systems in addition to Exchange • Smart host cannot resolve the recipient’s name; message returned with a nondelivery report (NDR)

  16. SMTP VIRTUAL SERVER CONFIGURED AS A RELAY HOST • Configure an SMTP virtual server as an inbound relay host • Gives Exchange Server 2003 smart host capabilities • Can configure other SMTP servers to use the virtual server as their smart host • Virtual server resolves the recipient’s SMTP domain name through DNS and delivers the messages

  17. LIMIT THE SERVERS THAT CAN RELAY E-MAIL MESSAGES • Specify who or what can relay e-mail messages through your organization: • Computers • Groups of computers • Domains • Prevent unwanted SMTP hosts from using your SMTP host as a relay agent • Stops third parties from relaying bulk unsolicited commercial e-mail

  18. SMTP CONNECTOR CONFIGURED TO USE A SMART HOST • By default SMTP Connector uses DNS • Can configure connector to forward all outbound mail to a smart host • Typically SMTP configuration done on connector rather than virtual server

  19. CONFIGURING DOMAINS TO WHICH YOU WANT TO RELAY MESSAGES • Can limit domains to which you relay messages • Useful when organization has multiple SMTP messaging systems and domain names • SMTP host can accept messages from any domain but then forward them only to specific domains

  20. VERIFYING A CONNECTION BETWEEN AN SMTP CONNECTOR AND A SMART HOST • Send an e-mail message to an unresolvable address on the smart host • Verify the connection object in the queue

  21. CONFIGURING CONNECTIONS ON AN SMTP VIRTUAL SERVER • Incoming: • Limit Number Of Connections To • Connection Time-Out (Minutes) • Outgoing: • Limit Connections To • Time-Out (Minutes) • Limit Connections Per Domain To • TCP Port

  22. SMTP SECURITY • Authentication • Encryption • Reverse DNS lookup

  23. AUTHENTICATION

  24. ENCRYPTION

  25. REVERSE DNS LOOKUP • IP spoofing: • Attacker impersonates a trusted host • Uses its IP address • Reverse DNS lookup: • Resolves IP address to a host name or FQDN • Confirms that the sender’s IP address is from the correct network • Result written into the message’s SMTP header

  26. RESTRICTING INTERNET E-MAIL

  27. RELAYING • Permits mail for another organization to be forwarded • Disabled by default • Required for interfacing with other SMTP mail systems • Required to allow IMAP4 and POP3 clients to send mail

  28. OPEN RELAYING • Organization configured to allow relaying by default • Open relaying allows propagation of junk mail

  29. CONFIGURING RELAYING • Can restrict using discretionary access control lists (DACLs) • Safer to create additional SMTP virtual server

  30. RETRIEVING E-MAIL FROM AN ISP • Typically over a nonpersistent connection • Configure the on-demand dial-up connection in Routing and Remote Access Service • Configure ISP’s Exchange server as smart host • Pull e-mail by using the turn or etrn command • Advanced tab of SMTP Connector’s Properties dialog box • Request ETRN/TURN when sending messages

  31. MESSAGE DELIVERY FAILURES • Identify where failure occurred • SMTP host unable to deliver: • Test using telnet • DNS problem: • Test using nslookup

  32. OTHER SMTP MESSAGING SYSTEMS • If connectors do not exist: • Obtain third-party gateways • Use Microsoft Exchange 5.5 connectors • Microsoft Mail: • Configure Exchange 2000 Server for directory synchronization

  33. GLOBAL SETTINGS • Configure systemwide settings • Overridden by: • Virtual server settings • Per-user settings

  34. SMTP POLICY ON A DOMAIN NODE • Does not create a new domain • Used when sending messages in a format suitable for another domain • Can be used to send mail to a partner organization • Can be used for interdomain mail within the same forest

  35. CONFIGURING AN SMTP POLICY

  36. MAILBOX DEFAULTS • Mailbox defaults apply to all mailboxes • Per-user settings apply to individual mailboxes • Widely used to prevent bottlenecks in the Exchange routing engine • Message size limits can apply to inbound or outbound messages • Recipient limits apply to all messages

  37. PER-USER SETTINGS FOR OUTLOOK WEB ACCESS

  38. PER-USER SETTINGS FOR IMAP4 AND POP3

  39. SUMMARY • How SMTP and ESMTP work • Identifying Exchange servers and connecting to the Internet • SMTP virtual servers, connectors, relays, and smart hosts • Security: authentication, encryption, reverse DNS lookup • Global settings and SMTP policies • Per-user settings

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