HELO

The HELO command is used to identify the domain name of the sending host to SMTP. This command is used to initiate a mail transaction, and must be sent (once) before a MAIL FROM: command is used.
Read syntax diagramSkip visual syntax diagramHELOdomain_name
Operand
Description
domain_name
Specifies the domain name of the sending host. The domain_name may be specified as either:
  • a domain name
  • an IP address in decimal integer form that is prefixed by the number or (US) pound sign (# or X'7B')
  • an IP address in dotted-decimal form, enclosed in brackets.
  • the string IPv6: followed by an IPv6 address in full or compressed form (IPv6 mapped IPv4 addresses are acceptable).

When HELO commands are received over a TCP connection, SMTP replies with the message 250 SMTP_server_domain is my domain name. The SMTP server client verification exit or built-in client verification function can be used to determine if the provided domain_name matches the client IP address and to include the result of that determination in the mail headers. See z/VM: TCP/IP Planning and Customization for detailed information about configuring SMTP to use this support.

When HELO commands are received over a batch SMTP connection, SMTP replies with the message 250 SMTP_server_domain is my domain name. Additional text is included with this message that indicates whether the provided domain_name does or does not match the host name of the spool file origination point. The 250 reply code indicates the HELO command is accepted and that SMTP commands can continue to be sent and received.