Hi Pavithra,
Enable the debug trace for below locations and get the debug traces to see what went wrong. Check this sap note 856599 - FAQ: XI 3.0 / PI 7.0 / PI 7.1 Mail Adapter
com.sap. aii.adapter.mail* - Mail Adapter Bean
com.sap. aii.af.sdk.xi.net* - Connection with mail servers
com.sap. aii.af.sdk.xi.srt* - Mail Message Processing
com.sap. aii.af.sdk.xi.mo.xmb* - Detailed XI Mail Message Processing
Regards,
Praveen.