Problems with Exim hosts_require_tls config

I'm trying to enforce TLS for out going mail to a single host. I'm no exim expert, in fact I've never even used it, it was all set up by the previous developer.

I just assumed inserting hosts_require_tls = example.co.uk in exmin.conf and restarting the service would work. But when I add this line the service wont start. I checked in the "panic" error log after trying to start the service and it contains

"2011-08-02 12:20:18 Exim configuration error in line 150 of /etc/exim.conf: main option "hosts_require_tls" unknown"

So I'开发者_开发知识库m obviously being dumb and putting it in the wrong config file or something. Any help would be greatly appreciated. Thanks! :-)

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The setting has to be put in the corresponding transport configuration section, probably

remote_smtp:
    driver = smtp
    hosts_require_tls = example.co.uk

by default. Not in the main configuration (where it is unknown).