[exim] How to verify certificate in transport

Hello,

I want to send mails to a smarthost encrypted. My attempts to do it
over smtps failed, I suppose this can't be done with exim4.

So I tried to force TLS. I already have added a “hosts_require_tls” to
the “remote_smtp_smarthost” transport to prevent unencrypted delivery.

I tried adding “tls_certificate = …/bla.crt” to make exim check the
server-certificate against bla.crt, but this gives me:

TLS error on connection to smarthost [ip] (cert/key setup:
cert=…/bla.crt key=…/bla.crt): Base64 unexpected header error.

So how do I make exim to check the certificate to prevent
man-in-the-middle attacks?

    MfG
    bmg

-- 
„Des is völlig wurscht, was heut beschlos- | M G Berberich
 sen wird: I bin sowieso dagegn!“          | berberic@???
(SPD-Stadtrat Kurt Schindler; Regensburg)  | www.fmi.uni-passau.de/~berberic