help with sieve

[dovecot at paulkoppen.com]

Dear Dovecot / Pigeonhole community,

I have a very specific issue, but trying to solve this for a full day, I 
am now getting so bold from pulling my hairs out, I thought it was time 
I asked for help. I hope this is a good place for that.

At my hosting provider, who have been extremely helpful by the way but 
are not specifically skilled in Sieve, I have a catch-all address set 
up: *@domain.org (where * is literal), with a sieve script to control 
how messages are forwarded. Currently my rules are of the form:

if address :localpart :is ["To","Cc","Bcc"] ["name1", "name2", ...] { 
... }

This works most of the time, but sometimes the messages are not directly 
addressed to me and so they slip through the filters. I figured that 
using envelope would solve this, so I require envelope and then do:

if envelope :localpart :is "To" ["name1", "name2", ...] { ... }

But this fails. After endlessly trying different combinations I figured 
out that the reason for failure is that the envelope believes the "To" 
is actually "*@domain.org", so it is never going to match any of the 
names. However, the following test succeeds:

if header :contains "Envelope-To" "name1@" { ... }

 From this I deduce that a previous script has already done the 
conversion from name1 to *, and at the point where my sieve script is 
run the envelope picks up the *@domain.org address, leaving the 
Envelope-To header for what it is. But I am new to this.

Is that likely to be the case? Is it a common sieve set-up? And most 
importantly, is there a better way around the issue than testing header 
:contains?

With kind regards,
Paul