[Exim] Exim 4.20 - sender_domains option doesn't work

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When I try to use the "sender_domains = " option, Exim 4.20 complains with the message:

option "sender_domains" unknown

I tried following the = with a domain name and with a file which contains domain names, as in:

sender_domains = xxx.yyy.com

sender_domains = /etc/exim/filename

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