Hi Aanjan,
The error is error log is as below and mail server extension I got it from Market place.ThingWorx IoT Marketplace » Mail
[L: ERROR] [O: E.c.t.w.ExtensionPackageUploader] [I: ] [U: SuperUser] [S: ] [T: http-nio-80-exec-6] (see error log details) [context: Extension Exception: [package: Mail_Extensions, error: An error occurred while registering resources.]][message: [package: Mail_Extensions, error: An error occurred while registering resources.]] com.thingworx.extensibility.ExtensibilityException: [package: Mail_Extensions, error: An error occurred while registering resources.]
at com.thingworx.webservices.ExtensionPackageUploader.unpack(ExtensionPackageUploader.java:181) ~[thingworx-all-6.5.5-b473.jar:na]
at com.thingworx.webservices.ExtensionPackageUploader.service(ExtensionPackageUploader.java:95) ~[thingworx-all-6.5.5-b473.jar:na]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) [servlet-api.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) [catalina.jar:8.0.30]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.30]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-websocket.jar:8.0.30]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.30]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.30]
at com.thingworx.security.contenttype.ContentTypeFilter.doFilter(ContentTypeFilter.java:81) [thingworx-all-6.5.5-b473.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.30]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.30]
at com.thingworx.security.filter.ValidationFilter.doFilter(ValidationFilter.java:20) [thingworx-all-6.5.5-b473.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.30]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.30]
at com.thingworx.security.authentication.AuthenticationFilter.propagateRequest(AuthenticationFilter.java:343) [thingworx-all-6.5.5-b473.jar:na]
at com.thingworx.security.authentication.AuthenticationFilter.doFilter(AuthenticationFilter.java:145) [thingworx-all-6.5.5-b473.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.30]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.30]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212) [catalina.jar:8.0.30]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) [catalina.jar:8.0.30]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) [catalina.jar:8.0.30]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) [catalina.jar:8.0.30]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [catalina.jar:8.0.30]
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616) [catalina.jar:8.0.30]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) [catalina.jar:8.0.30]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:521) [catalina.jar:8.0.30]
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1096) [tomcat-coyote.jar:8.0.30]
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:674) [tomcat-coyote.jar:8.0.30]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500) [tomcat-coyote.jar:8.0.30]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456) [tomcat-coyote.jar:8.0.30]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_65]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_65]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-util.jar:8.0.30]
at java.lang.Thread.run(Unknown Source) [na:1.8.0_65]
