PMDF System Manager's Guide

Any occurrences of $U in the template are replaced with the username (local part) from the original address. Note that usernames of the form a."b" will be replaced by "a.b" as current Internet standardization work is deprecating the former syntax from RFC 822 and it is expected that the latter usage will become mandatory in future.

Any occurrences of $0U in the template are replaced with the username from the original address, minus any subaddress (and subaddress indication character such as +). Any occurrences of $1U in the template are replaced with the subaddress and subaddress indication character, if any, from the original address. (See Section 2.3.4.71 and Section 3.1.1.6 for background on subaddresses.) So note that $0U and $1U are complementary pieces of the username, with $0U$1U being equivalent to a simple $U.

$0U and $1U are most commonly used in PMDF MessageStore rewrite rules, where it is common to force the account portion of the local part to lowercase while retaining original case in the subaddress since the subaddress in a PMDF MessageStore address indicates a folder name. For instance, a rewrite rule:

msgstore.example.com $\$0U$_$1U@msgstore.example.com

will cause an address such as nAmE@msgstore.example.com to be transformed (rewritten) to name@msgstore.example.com, while an address such as nAmE+sUbAdDrEsS@msgstore.example.com would be transformed to name+sUbAdDrEsS@msgstore.example.com.