User case MTA option

Alias and address MTA options:  (0 or 1)
The  MTA option causes some effects of forcing user names to lower case (on certain "local" sorts of channels), affects the forcing-to-lowercase of  variants of "postmaster",  and can influence the sorting of addresses. The default is 1, which has the general meaning that case sensitive user names are permitted, except that any "postmaster" variants are forced to lower case. If set to 0, and if the   channel option is set either explicitly on a channel (or implicitly forced as with the l channel), then general user names matching that channel will be forced to lower case.

The  MTA option also potentially, depending upon other conditions, may affect the sorting of addresses.

See also:
 * Postmaster addresses
 * localbehavior Option
 * Alias and address MTA options
 * Notification message MTA options