Domain/host exist check failing

Hi there. First of all thanks a lot for the module. I've been using it for three years and very happy. I now found out that it did not validate existing e-mails in some situations and unfortunately had to disable it for customer friendliness. I get an error saying: Email host xxx does not seem valid, it did not answer. (The address in question was provided by bluewin.ch.) I cannot pin down the problem precisely as I do not understand how your checking works but found out the provider does not accept pings.

Thanks in advance. Regards, s0s