sub alias_to_emailaddress {
 my ($alias) = @_;    #-- e.g. "Bob";

 #-- query your DB or start with a hash-lookup for testing...
 my %alias2email = ( 'BOB'  => 'some@email.com',
                     'TIM'  => 'test@cork.com',
                   );

 #-- maybe normalise your alias first?  
 my $email = $alias2email{ uc $alias };

 #---- now add some error handling...
 
 #-- perlhaps you can use a default?
 #  $email //= 'bugreport2self@myhost.com';

 #-- throw an exception (catch with 'eval' later) 
 # die "No email-address found for '$alias'!" unless $email;

 return $email;
}