Comment 98 for bug 119899

As an addition to my comment #86, I've noticed the following:

If I compact all folders (which apparently rebuilds the .msf files), the
filters on *some* custom headers start working!

There's at least one exception, though: filtering on a "Sender:" header.
It looks like maybe there's an internal "Sender", which overrides it? I
vaguely remember another bug report that mentions this, I'll have to go
hunt it down.

In one of such cases, the exact condition in msgFilterRules.dat is:

  condition="OR (\"sender\",contains,<email address hidden>)"

and messages from this particular mailing list truly contain this
header:

  Sender: <email address hidden>

However, TB3 doesn't filter on this condition.