Hello,

until it (may or may not) get added, you can use the following:
Code:
  
msgchans {
  var %msg = $2-
  tokenize 44 $1
  while ($0) { if $left($1,1) == $chr(35) { msg $1 %msg } | tokenize 32 $2- } 
}

Usage: /msgchans #chan1,#chan2,#chan3 message

Note that you can rename this alias to whatever name you want, though if you change it to "alias msg", note that it will override the normal /msg command, unless you do /!msg, which will use mIRC's default /msg command.

Greetz

Gone.