sieve filter based on utf-8 encoded text part of address

[Hans-Peter Jansen]

Hi,

I try to filter based on the text part of an utf-8 encoded address, but the 
string matches neither decoded nor encoded.

This is a periodic mail from one of a couple of different routers, where only 
the text part defines a useful origin:

From: "=?UTF-8?B?RlJJVFohQm94IDc0OTAgU0ZK?=" <my at address>

which decodes to:

FRITZ!Box 7490 SFJ <my at address>

sieve filter script except:

; my requirements
require ["fileinto", "reject", "regex", "vacation"];

; the filter rule
if address :contains "From" [
	"FRITZ!Box 7490 SFJ",
	"=?UTF-8?B?RlJJVFohQm94IDc0OTAgU0ZK?="
] {
    fileinto "INBOX.some.folder";
    stop;
}

How do I do this correctly?

Thanks in advance,
Pete