while (<DATA>){
  chomp;
  my %rec=();
  while ( /
       ([^:]*)    # any amount of non ":"'s -better as ([A-Z0-9]*)?
          :       # followed by a colon
       ([^%]*)    # any amount of non "%"'s
       %{0,1}     # followed by 0 or 1 % characters
      /xg ){
         $rec{$1}=$2;
  }
  print $rec{SMTP}, "\n";  # for example
}

__DATA__
SMTP:makeusbetter@domain.com%X400:c=US;a= ;p=domain ;o=domain;s=makeusbetter;%CCMAIL:makeusbetter at domain%
CCMAIL:Hunter, Sandy at domain%MS:domainin/domain/sandy%SMTP:sandyh@domain.com%X400:c=US;a= ;p=domain