Lately we are receiving multiple requests with mail fetching issue. We have found that it occurs particularly with the Office 365 users. The issue is due to an update in their SSL certificate. 

Here's the error trace we see on the logs, 

Exception when connecting to store.|javax.mail.MessagingException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target;
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

Please follow the steps below to fix it, 

1. Download the file from the link given below and extract it to the Service Desk Plus Home directory.
   https://uploads.zohocorp.com/Internal_Useruploads/dnd/ServiceDesk_Plus/2016_02_03_11_25_23_o_1acqu0dua1tidbq1kni1llri9g1.tar.gz
2. Run the Extracted batch file from the command prompt using the syntax given below.
   syntax:- gencert.bat (hostname of the mail server):(port)
   eg:-
   cmd> gencert.bat sdpexchnage.com:995
3. You will receive an exception PKIX. On supplying the value 1, a file called jssecacerts is generated in the ServiceDesk Plus Home Directory.
4. Copy the jssecacerts file under jre\lib\security folder and restart ServiceDesk Plus application.
5. Fill in the values under Mail Server Settings. Start fetching mails to check the functionality.

ServiceDesk Plus