in reply to Find error message starting at line after last error
I must be missing something here...
You're slurping it line-by-line with <$tail>, and emailing the lines containing the error. What are you resetting file position for? The loop will just proceed to the next line automatically. Why close and reopen? I guess the log is being rotated underneath?
For this sort of thing I'd probably read from a 'tail -F' pipe instead and keep the perl part trivial. Or use any of the multitude of CPAN tail modules, rather than trying to reimplement tail all over again.