Actually I have some production code that does this, with Office365 even. I've been meaning to clean it up a bit to be less work-specific and publish it on CPAN but never got around to it. But, here's some snippets that might help you:

   my $conn= Net::IMAP::Simple->new(
      $host,
      port   => $port,
      ($port == 993? (
         use_ssl => 1,
         ssl_options => [
            SSL_verify_mode => IO::Socket::SSL::SSL_VERIFY_PEER()
         ]
      ) : ()),
      debug  => $log->is_trace,
   )
      or _logcroak("Cannot connect to server $host: $Net::IMAP::Simple
+::errstr");
   
   if ($port != 993) {
      $conn->starttls
         or _logcroak("Can't start TLS after conencting to $host port 
+$port: ".$conn->errstr);
   }
   
   $conn->login($user, $self->login_pass)
      or _logcroak("Can't authenticate as $user to server $host: ".$co
+nn->errstr);
   $log->info("Logged in as ".$user);
   
   my $mbox= $url->path;
   $mbox= 'INBOX' unless defined $mbox and length $mbox and $mbox ne '
+/';
   $conn->select($mbox)
      or _logcroak("Can't select folder $mbox");
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Then, in a loop:

   $conn->select; # call select again to refresh message list
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   $msg_ids= [ $conn->search($imap_query) ];
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   for my $msgid (@$msglist) {
      $log->debug("Msg $msgid");
      my $header_lines= $conn->top($msgid);
      my $head= MIME::Head->from_file(\join('', @$header_lines)) or di
+e;
      ...
      # filtering code goes here, which inspects headers
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     # this is the code that pulls in the whole message
     my $fh= $conn->getfh($msgid) || \
      _logcroak("Failed to get message file handle: ".$conn->errstr);
     my $p= MIME::Parser->new;
     $p->output_to_core(1);
     return $p->parse($fh);
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I'll add that Email::MIME has a nicer interface than MIME::Parser but I had some particular edge cases where MIME::Parser worked better for me. I recommend starting with Email::MIME and see if it works for you.

The part where you want to search only unread messages is done using the IMAP query, and IMAP::Simple describes that well enough. Also I think Office365 doesn't support IMAP unless you specifically enable it somewhere in your account preferences.