email scheduler help how to configure

Hi I am running jasper server ce 3.7.0

I have configured the js.quartz.properties file to allow the emailing and scheduling of reports, I have used telnet and SMTP to test my username etc and have sent a test email no problem, but when I try and schedule a report and email it I get the following error which I don't understand.

Mail server connection failed; nested exception is javax.mail.MessagingException: Can't send command to SMTP host;
nested exception is:
 javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
        at org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:419)
        at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:342)
        at org.springframework.mail.javamail.JavaMailSenderImpl.send(JavaMailSenderImpl.java:338)
        at com.jaspersoft.jasperserver.api.engine.scheduling.quartz.ReportExecutionJob.sendMailNotification(ReportExecutionJob.java:1259)
 

It's a ms exchange server I am trying to speak to, but should that be an issue for simple SMTP???

any thoughts or ideas much appreciated.

thanks

Jasemilly