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