The problem is that there can be hundreds of original senders. Having that many filehandles open is certain to be problematic....Should I just risk opening a zillion filehandles?

On what do you base you supposition that having lots of file descriptors open is a problem? What risks do you perceive? You assert but do you test. By default on Win2K you can have 509, on Linux 1021. 3 handles are used for STDIN, STDOUT, STDERR, so there are 512 and 1024 handles respectively available.

C:\tmp>perl -e "open ++$fh, '>', $fh or die qq'$fh $!\n' for 1..$ARGV[
+0]" 512
510

[root@devel3 tmp]# perl -e 'open ++$fh, ">", $fh or die "$fh $!\n" for
+  1..$ARGV[0]' 1024
1022 Too many open files
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But so what? Just increase the number if you need to. On Linux:

[root@devel3 tmp]# ulimit -n 65535
[root@devel3 tmp]# perl -e 'open ++$fh, ">", $fh or die "$fh $!\n" for
+  1..$ARGV[0]' 2048
[root@devel3 tmp]# ls 204?
2040  2041  2042  2043  2044  2045  2046  2047  2048
[root@devel3 tmp]#
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It is not actually the number of open file handles that will cause an issue. Depending on the underlying file system you will start to get issues if you go over10-20,000 files in a single direcotry with ext2/3. Reiser FS does not care.