The attachment you forwarded me, is not someone trying to reply
to your message. It is your own message, sent back to you
because one of the people on the maillist (email@example.com in
this case) could not receive mail.
Usually this happens because someone's e-mail address has
changed, but they forgot to update the maillist too, so mail sent
to the old address, bounces. But in this case the error message
was "Remote protocol error", which sounds like a system problem
at America OnLine (aol.com).
Regardless of what caused the error, if the mail is
undeliverable, it is usually sent back to the sender or to a
"Reply-to" or "Errors-to" address. Many of these are sent to
si-admin@silab.Eng.Sun.COM, but some of them find their way back
to the originator (you). It's unfortunate, but that's life on
the Internet. I get them all the time from the SI maillist.
You can ignore them.
Regarding your criteria, I would say that 0.8V for ringback is way too much for TTL and LVTTL, if you define ringback as the magnitude that the voltage crosses back past Vih(min) or Vil(max). 0.3V or less, sounds better. Regular 5V CMOS can probably tolerate more.
Keep in mind that ringback generally doesn't matter until the point in time when you need your inputs to be stable. That is, if it is a data (non-clock) signal, there will be Setup and Hold times that must be observed. Outside of the interval between them, the input can ringback any amount and it may make no difference (unless it causes metastability that doesn't stop once the input stabilizes; or if the input sits right around threshold and causes excessive currents from VDD to VSS).