I am having an approval process where whenever a record is saved i want to use a trigger and send for email approval. I want to use inbound and outbound email services to update fields. I will send an approval form with a checkbox if a user replies to message it must update checkbox field and i want to write an workflow to send email that it was approved. How can i easily do the functionality instead of such long process.
This is something that can readily be done via the API using Approval Processes and Workflow. There's no need to write any triggers, create email services, etc. and doing so would be a poor use of Salesforce's resources and features. How to do what you want is described quite well in Force.com Fundamentals in the tutorials that take you through the process of creating a recruiting app.