Warning window when accessing private server with SSL

[Lutz Urban]

When accessing my private email server using SSL I always
receive a window with a warning message:

The server you are connected to is using a security
certificate that could not be verified.
A certificate chain processed correctly, but terminated in
a route certificate which is not trusted by the trust
provider.
Do you want to continue using this server ?

Is it possible to permanently get rid of it ?

Regards

Lutz