V -- Configuration Version Level

To provide compatibility with old configuration files, the V line has been added to define some very basic semantics of the configuration file. These are not intended to be long term supports; rather, they describe compatibility features which will probably be removed in future releases.

N.B.: these version levels have nothing to do with the version number on the files. For example, as of this writing version 8 config files (specifically, 8.7) used version level 6 configurations.

Old configuration files are defined as version level one. Version level two files make the following changes:

  1. Host name canonification ($[ ... $]) appends a dot if the name is recognized; this gives the config file a way of finding out if anything matched. (Actually, this just initializes the host map with the -a. flag -- you can reset it to anything you prefer by declaring the map explicitly.)
  2. Default host name extension is consistent throughout processing; version level one configurations turned off domain extension (that is, adding the local domain name) during certain points in processing. Version level two configurations are expected to include a trailing dot to indicate that the name is already canonical.
  3. Local names that are not aliases are passed through a new distinguished ruleset five; this can be used to append a local relay. This behaviour can be prevented by resolving the local name with an initial `@'. That is, something that resolves to a local mailer and a user name of vikki will be passed through ruleset five, but a user name of @vikki will have the `@' stripped, will not be passed through ruleset five, but will otherwise be treated the same as the prior example. The expectation is that this might be used to implement a policy where mail sent to vikki was handled by a central hub, but mail sent to vikki@localhost was delivered directly.

Version level three files allow # initiated comments on all lines. Exceptions are backslash escaped # marks and the $# syntax.

Version level four configurations are completely equivalent to level three for historical reasons.

Version level five configuration files change the default definition of $w to be just the first component of the hostname.

Version level six configuration files change many of the local processing options (such as aliasing and matching the beginning of the address for `|' characters) to be mailer flags; this allows fine-grained control over the special local processing. Level six configuration files may also use long option names. The ColonOkInAddr option (to allow colons in the local-part of addresses) defaults on for lower numbered configuration files; the configuration file requires some additional intelligence to properly handle the RFC 822 group construct.

The V line may have an optional / vendor to indicate that this configuration file uses modifications specific to a particular vendor[19]. You may use /Berkeley to emphasize that this configuration file uses the Berkeley dialect of sendmail.


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