This is mainly superficial, but there are some noteworthy comments. 
unless ($^O =~ /aix/) { die ... }
# might be better as


die ... unless $^O =~ /aix/;

[download]
I'm not sure about that whole $recipient thing. Are you expecting an argument? 
my $sequence_number = shift || die ...;
# technically, you want 'or' instead of '||' here

open (ERROR, "/usr/bin/errpt -g -l $sequence_number |");
# you don't check to see if it opened properly...
# nor do you ensure the safety of the variable
# if I enter '; rm -rf' here, you're in trouble


my ($sequence_number) = shift =~ /(\d+)/
  or die ...;
open ERROR, "/usr/bin/errpt -g -l $sequence_number |"
  or die "can't run errpt -g -l $sequence_number: $!";

[download]
I'm going to idiomatize your while-loop. 
while (<ERROR>) {
  $message{host} = (split)[1], next if /^el_nodeid/;
  $message{drive} = (split)[1], next if /^el_resource/;
  $message{detail} = (split)[1], next if /^el_detail_data/;
}

[download]
Your hex-to-ascii stuff can be replaced by using "H*" instead of "C". The only other thing I'd change is your @mail array and ALL those sprintf()s. 
printf SENDMAIL "%-16s: %-20s\n" => @$_ for
  ["Sequence Number" => $sequence_number],
  [ Host => $message{host} ],
  [ Drive => $message{drive} ],
  [ Model => $message{model} ],
  [ Microcode => $message{mml} ],
  [ "Message Type" => $message{type} ],
  [ "Message Code" => $message{code} ],
  [ Severity => $message{severity} ],

  $message{type} eq "SIM" ? (
    [ "First FSC" => $message{first_fsc} ],
    [ "Last FSC" => $message{last_fsc} ],
  ) : (
    [ VOLSER => $message{volser} ],
  );

[download]
It's condensed somewhat, and the data structure still represents the pairing between text and variable. And, if you need to change the format, you change it once.

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

In reply to Re: how can this be improved? by japhy
in thread how can this be improved? by blueflashlight

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