I see no database disconnect here. This error will be more noticable when you (and you really should :) ) turn on warnings.
I see no use of sendmail objects here. (although it might be importing something; I'm not so familiar with it)
Your SQL statements could benefit from a for loop, here's one way (among many) for your INSERT statement:

my @ins_fields= ("log");
my @ins_values= ("''");
for (1..25) {
    $writer[$_ -1] = "value of writer". ($_-1) ;
    push @ins_fields, "log$_";
    push @ins_values, $writer[$_ -1];
}
my $ins_fields = join ",", @ins_fields;
my $ins_values = join ",", @ins_values;
print "INSERT INTO $log ($ins_fields)\nVALUES ($ins_values)";
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There are other ways of doing this, of course, and they're all fun to discover ;-)
for your series of regexen :

        $findings=~s/,//g;
        $findings=~s/ /_/g;
        $findings=~s/\///g;
        $log="$findings";
        $log=~s/:/_/g;
        $log=~s/\./_/g;
        $log=~s/___/_/g;
        $log=~s/__/_/g;
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some of these can be 'optimized' by using tr///; always consider this when you have a direct 1-to-1 relationship between characters in and characters out, or when deleting chars. Your final 2 can be reduced to one regex, whose form depends on the answer to "are series of 4 or more underscores possible? would they be relevant in ways that 2 and 3 aren't?" Take a look at this snippet :

for (1..10) {
    my $foo = "_" x $_;
    $foo =~ s/_+/_/;
    print "method one : $foo\n";

    my $foo = "__" x $_;
    $foo =~ s/___?/_/;
    print "method two : $foo\n";
}
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The first one will take up any number of underscores and replace with a single underscore. The second will look for only two or three in a row, if there's 4 or more, it doesn't care. Whether this is relevant depends on your data.
Be sure to check the results of $sql->execute() -- if it's dying silently, what are the ramifications? use something like $sql->execute() || warn "SQL Execution failed! $DBI::errstr\nscript is $script";
Ok?