You need to set data types values as below for reading the mail.
Check this link for more details - http://help.adobe.com/en_US/livecycle/9.0/workbenchHelp/help.htm?content=001463.html
Also see "Use an e-mail start point" @ http://www.adobe.com/devnet/livecycle/videotraining.html
Thank You for your replay,
Actually I am not able to set the data types values as you mensioned, How can I set that?
for variables, I have given the datatype as string, and I have pasted '%BODY%' to one of my input variable, still when a new mail comes, I am not getting the mail body.
We had this issue with email formats other than plain text. Can you try the current process with a plain text email?. If this still having issues double check the variables and settings of the process. Please check the attached image for the settings of email process and adminUI of the variables used.