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SMTP Commands

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.