well do you think the certificate is from an impersonator? Or is it from your hosting company or anti virus program. I ran a test on the server. It is basically a disaster security wise. See https://www.immuniweb.com/ssl/smtp.plateautel.net/otAh2P0U/ The SSL certificate is self signed, so has no web of trust attached. The cypher used has been ended as simply not safe (SHA1) The cypher key length is about 8 years out of date at 1024bits. It should be at least 2048bits I suggest you contact the people who run the server and point then to the issues in the report so they can correct them, or you could stop using encrypted connections.