The following table lists the SMTP commands that are provided by the Microsoft Windowsยฎ SMTP service (SMTPSVC).
SMTP commands
| SMTP command | Command function |
| HELO | Sent ย by a client to identify itself, usually with a domain name. |
| EHLO | Enables ย the server to identify its support for Extended Simple Mail Transfer Protocol ย (ESMTP) commands. |
| MAIL ย FROM | Identifies ย the sender of the message; used in the form MAIL FROM:. |
| RCPT ย TO | Identifies ย the message recipients; used in the form RCPT TO:. |
| TURN | Allows ย the client and server to switch roles and send mail in the reverse direction ย without having to establish a new connection. |
| ATRN | The ย ATRN (Authenticated TURN) command optionally takes one or more domains as a ย parameter. The ATRN command must be rejected if the session has not been ย authenticated. |
| SIZE | Provides ย a mechanism by which the SMTP server can indicate the maximum size message ย supported. Compliant servers must provide size extensions to indicate the ย maximum size message that can be accepted. Clients should not send messages ย that are larger than the size indicated by the server. |
| ETRN | An ย extension of SMTP. ETRN is sent by an SMTP server to request that another ย server send any e-mail messages that it has. |
| PIPELINING | Provides ย the ability to send a stream of commands without waiting for a response after ย each command. |
| CHUNKING | An ย ESMTP command that replaces the DATA command. So that the SMTP host does not ย have to continuously scan for the end of the data, this command sends a BDAT ย command with an argument that contains the total number of bytes in a ย message. The receiving server counts the bytes in the message and, when the ย message size equals the value sent by the BDAT command, the server assumes it ย has received all of the message data. |
| DATA | Sent ย by a client to initiate the transfer of message content. |
| DSN | An ย ESMTP command that enables delivery status notifications. |
| RSET | Nullifies ย the entire message transaction and resets the buffer. |
| VRFY | Verifies ย that a mailbox is available for message delivery; for example, vrfy ted ย verifies that a mailbox for Ted resides on the local server. This command is ย off by default in Exchange implementations. |
| HELP | Returns ย a list of commands that are supported by the SMTP service. |
| QUIT | Terminates ย the session. |
Extended SMTP commands
| Extended SMTP command | Command function |
| X-EXPS ย GSSAPI | A ย method that is used by Microsoft Exchange Serverย 2003 and ย Exchangeย 2000 Server servers to authenticate. |
| X-EXPS=LOGIN | A ย method that is used by Exchangeย 2000 and Exchangeย 2003 servers to ย authenticate. |
| X-EXCH50 | Provides ย the ability to propagate message properties during server-to-server ย communication. |
| X-LINK2STATE | Adds ย support for link state routing in Exchange. |
Ports used by Exchange
| Protocol | Port | Description |
| SMTP | TCP: ย 25 | The ย SMTP service uses TCP portย 25. |
| DNS | TCP/UDP: ย 53 | DNS ย listens on port 53. Domain controllers use this port. |
| LSA | TCP: ย 691 | The ย Microsoft Exchange Routing Engine service (RESvc) listens for routing link ย state information on this port. |
| LDAP | TCP/UPD: ย 389 | Lightweight ย directory access protocol (LDAP) used by Microsoft Active Directoryยฎ ย directory service, Active Directory Connector, and the Microsoft Exchange ย Serverย 5.5 directory use this port. |
| LDAP/SSL | TCP/UDP: ย 636 | LDAP ย over Secure Sockets Layer (SSL) uses this port. |
| LDAP | TCP/UDP: ย 379 | The ย Site Replication Service (SRS) uses this port. |
| LDAP | TCP/UDP: ย 390 | This ย is the recommended alternate port to configure the Exchange Serverย 5.5 ย LDAP protocol when Exchange Serverย 5.5 is running on an Active Directory ย domain controller. |
| LDAP | TCP: ย 3268 | Global ย catalog. The Windowsย 2000 and Windows Serverย 2003 Active Directory ย global catalog (a domain controller “role”) listens on TCP ย portย 3268. |
| LDAP/SSLPort | TCP: ย 3269 | Global ย catalog over SSL. Applications that connect to TCP portย 3269 of a global ย catalog server can transmit and receive SSL encrypted data. |
| IMAP4 | TCP: ย 143 | Internet ย Message Access Protocol (IMAP) uses this port. |
| IMAP4/SSL | TCP: ย 993 | IMAP4 ย over SSL uses this port. |
| POP3 | TCP: ย 110 | Post ย Office Protocol version 3 (POP3) uses this port. |
| POP3/SSL | TCP: ย 995 | POP3 ย over SSL uses this port. |
| NNTP | TCP: ย 119 | Network ย News Transfer Protocol (NNTP) uses this port. |
| NNTP/SSL | TCP: ย 563 | NNTP ย over SSL uses this port. |
| HTTP | TCP: ย 80 | HTTP ย uses this port. |
| HTTP/SSL | TCP: ย 443 | HTTP ย over SSL uses this port. |
