Expired certificated message in Outlook 2010 can't by-pass

In one of our compagny signature there is a link to a charity web site and now every time we send an email it tells us:"The validity of this web site or connection cannot be verify"
Then I have a "want to continue Yes No Display certificate"
I tried importing(installing) it but it just keeps coming back for everyone.
We have office 2010.
Is there a way to just stop it, something simple cause I have 40 users with that problem.
If I cannot find something, I'll just remove it from the signature
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When you open outlook you get a certificate popup?
philjansAuthor Commented:
No when I click on send an email with my special signature
is the certificate on the web site is self-signed. Install the certificate in trusted root certification authority and try.
philjansAuthor Commented:
I contacted the web site who had problem with their certificate and they updated it and now the problem is gone. Thanks for your help

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philjansAuthor Commented:
I fixed the problem at the source
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