Microsof Outlook

D

Dunc

When I press send to send an email, recieve message
saying "Invalid Certificate" message goes on to say
I do not have valid certificate to send these messages.
I go into "change security settings" and untick the boxes,
this allows me to then send the message. Trouble is that
when I send next message same thing happens again. How
can I stop this box appearing
 
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