[Brian]

We probably need a bit more info to figure out exactly what's going on, but one thing I've seen cause problems in the past is either of two things. One cause is when some white space characters accidentally got entered into OmniFocus' preferences. So instead of looking for "--", the app is checking for "<space>--" or "<tab>--" or something.

Another thing I've seen is where folks are forwarding along the emails, rather than redirecting or sending messages they wrote themselves. In that case, since the email starts with "Fwd: --" or something similar, it doesn't match the filter.

And of course, it just occurred to me that I may be duplicating tips that were in the other post that Bill pointed you at. Well, just in case it helps, I'll leave it here. :-)