sales:bob@foo.com
sales:joe@foo.com
retail:steve@bar.com
sales:debbie@foo.com
sales:john@foo.com
support:david@blah.com
retail:judy@bar.com
support:jose@blah.com

##</code><code>##

sales:bob@foo.com,joe@foo.com,debbie@foo.com,john@foo.com
retail:steve@bar.com,judy@bar.com
support:david@blah.com,jose@blah.com

##</code><code>##

%hash;
while (<>) {
    my ($dept,$email)=split(/:/);
    $hash{$dept}{'email'} = $email;
}