The -V command-line switch is used to specify the envelope identifier for the outgoing message. That identifier is called the ENVID and is part of the DSN extension to ESMTP. ENVID and the ${envid} sendmail macro are fully discussed in ${envid}.

The form of the -V command-line switch looks like this:

-Venvid
-V envid

Space between the -V and its argument is optional. The envid must be a legal ENVID identifier (${envid}). If an illegal character is specified in envid, the following error is printed, and that declaration is ignored:

Invalid syntax in -V flag