Domainvrfy, localvrfy, novrfy Channel Options

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Sending an SMTP VRFY command (domainvrfy, localvrfy, novrfy)

These options control the MTA's use of the VRFY command in its SMTP client. Under normal circumstances there is no reason for the MTA to issue a VRFY command as part of an SMTP dialogue - the SMTP MAIL TO command should perform the same function that VRFY does and return an appropriate error. However, while fairly rare, SMTP servers exist that will accept any address in a MAIL TO (and bounce it later), whereas they perform more extensive checking as part of a VRFY command.

Therefore the MTA can be configured to issue SMTP VRFY commands for each recipient address. The channel option domainvrfy causes the MTA to issue a VRFY command with a full address (e.g., user@host) as its argument. The localvrfy option causes the MTA to issue a VRFY command with just the local part of the address (e.g., user). novrfy is the default.

Note that while RFC 1123 updated RFC 821 to require support of the VRFY command so modern SMTP servers should have VRFY support, originally RFC 821 did not require that SMTP implementations support VRFY so obsolete SMTP implementations may not have any VRFY support at all. Also note that RFC 821 intentionally left it up to individual implementations to decide on the syntax of the VRFY argument---to decide, that is, what sorts of arguments would get successful responses. So relying on getting a successful response to any sort of VRFY command to determine whether or not to try submitting an address is not, in general, wise. Thus use of localvrfy or domainvrfy is normally only suitable on special channels sending to known special SMTP hosts with well-understood and special VRFY response behavior.