Welcome! Firstly reading your server list from a file:

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my $serverfile = 'servers.txt';

open (my $fh, '<', $serverfile) or die "can't open file $serverfile: $
+!";
chomp(my @servers = <$fh>);
close $fh;

print Dumper @servers;
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In the above example I use the Data::Dumper module to print the array, you obviously don't need this part. Also note the use of $! to tell you why trying to open the file failed. For further info take a look at open.

For sending mail I use the MIME::Lite module, example code in the documentation.

"That being said, I did manage to add the output to file element but it gave me an uninitialized value in concatenation error for $res"

Can you please post the exact error and the code which generates it? How do I post a question effectively? has tips on how to best achieve this around here.