Is there any one who has integrated outlook with appian to fetch mails and store

You can configure Appian to fetch mail from a mailserver like exchange or any imap server. Each fetched mail can start a process or be sent to a receive message node in a running process. From there you have access to the parts of the email.

Adding to Stefan's suggestion, you could then write your own Smart-Service to compile the parts of the Email that were fetched back into a *.msg file in Appian and then store in the KC, to make it available for the Users to download.

Configure email polling on your mail server which will read the incoming emails to your outlook and re direct it to Appian process model - which will have a listener email node to parse the email details and store it in Appian environment.