Hi Anuja,
This can be automated, but you may need some skill or help from difference domain.
Here what's the idea based on...
1) Process Chain can trigger by FM
2) FM can setup as RFC
3) In SAP you can create Web Service to call RFC
4) In many mail server, you can trigger application on mail receive, and web service is likely to support nowadays
So what you need to do is:
1) Create a FM to call the chain you need
2) Make sure this FM is RFC enabled
3) Make this RFC FM as web service
4) At mail server, write script to process email on receive, when receive a valid email trigger the web service
Regards
Bill