check_vrfy and check_expn

Validate VRFY and EXPN Policy rule set

The SMTP VRFY command is used to verify an email address. The SMTP EXPN command is used to expand an email address. They are used like this:

VRFY gw@wash.dc.gov
250 2.1.5 George Washington <gw@wash.dc.gov>
VRFY nosuchuser@wash.dc.gov
550 5.1.1 nosuchuser@wash.dc.gov... User unknown
EXPN all@wash.dc.gov
250-2.1.5 George Washington <gw@wash.dc.gov>
250 2.1.5 Andrew Jackson <aj@wash.dc.gov>

If sendmail can deliver to the address specified, it will respond with a 250, a DSN 2.1.5, the full name of the recipient (if known), and the normalized address. If the address is bad, sendmail will reply with a 550, a DSN 5.1.1, and the reason for the rejection of the request. If the request is to EXPN, and if the address expands to another or more addresses, as with an alias or a mailing list, sendmail will print each expanded-to address, one per line.

If your site has set goaway or novrfy for the PrivacyOptions option (PrivacyOptions on page 1065), sendmail will reject all SMTP VRFY commands with the following message:

252 2.5.2 Cannot VRFY user; try RCPT to attempt delivery (or try finger)

If your site has set goaway or noexpn for the PrivacyOptions option (PrivacyOptions on page 1065), sendmail will reject all SMTP EXPN commands with the following message:

502 5.7.0 Sorry, we do not allow this operation

The check_vrfy rule set can serve two useful functions. It can be used to print a different rejection message, and it can be used to ...

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