Option value syntax in legacy configuration

Option values are typically one of string, integer, or (less commonly) floating point, or in some cases comma-separated lists of one of the above types of values, or in other cases space-separated lists of one of the above types of values. Furthermore, some option values are further constrained, as for instance an integer in a particular range, or a string that corresponds to an LDAP attribute name or to a channel name; and some option values have additional semantics as for instance a bit-encoded integer, or a boolean integer. The type of value valid for an option depends upon the option&#x27;s requirements; the exact type required will be described for each option. The discussion below will touch on general syntax issues.

The length of the string specifying the option value (the length of the material to the right of the equal sign) is limited to 1024 characters; (prior to MS 6.2p8/6.3, the limit had been 256 characters). For options where the value involves substitution expansions (such as URL values using  URL substitution sequences), the limit after such expansion is (and has been) 1024 characters.

If an option accepts an integer value, a base may be specified using notation of the form, where   is the base expressed in base 10 and   is the actual value expressed in base.

Bit-encoded integer values are used for a number of options. A bit-encoded integer value may be written as any integer would be; however, it has additional semantics. In a bit-encoded integer value, each bit of the integer controls a different feature; thus a bit-encoded integer value expresses a whole set of enable/disable choices. The least significant bit is conventionally referred to a "bit 0". The integer value of each set bit is then two raised to the bit position power; for instance, setting bit 0 means adding 1 to the value, setting bit 1 means adding 2 to the value, setting bit 2 means adding 4 to the value, etc.

Boolean values may be specified either as a number, 0 (false) or 1 (true), or as a string "false" or "true".

Floating point values may be written either in usual decimal notation, for instance, 3.1416, or may be written using the common scientific exponential notation, for instance, 1.045E2 meaning 104.5. The exponent indicator may be any of the characters E, e, F, or f.

For string values, note that spaces are significant in values, including trailing spaces, as for certain options values with trailing spaces are meaningful. (However, as of Messaging Server 7.0, the MTA will attempt some "clean up" of certain option values, such as those for setting file names, or for reading options from the Dispatcher or  Job Controller  configuration files  -- where such "clean up" can potentially include removal of extraneous trailing spaces from the option value setting.)

See also:
 * MTA URL types
 * Legacy configuration MTA option file