Outlook

It sounds like you want to build a Portal.  I think this is an excellent use case.  So you need to create a Portal, which is a stand-alone public facing site that users can access without logging into Appian.  You could then configure a link in the email to the Portal page which then offers the user the buttons.  They click one of those, then Appian kicks off a process without the end user having to log in.

https://docs.appian.com/suite/help/22.1/portals-home.html

See if you think that could be a solution.

Thanks for sharing the info.

It seems to be we may require an additional license purchase to build Appian portal.

My requirement is:

I need to trigger an email notification from Appian system using Send E-Mail service and the notification will go to certain number of users with content like below. Now, when the user click on “APPROVE”  or “REJECT”, I need to update the status according in the Appian without login to the Appian.

Is there an alternate method / mechanism, using which I can integrate outlook with Appian or Appian with outlook.

Try using this - https://docs.appian.com/suite/help/22.1/Task_Viewer_Add-in_for_Microsoft_Outlook.html

It will work if you have SSO enabled 

I assume that doesn't work because you don't want to just avoid the login screen, you want to avoid the recipient even having an Appian account at all.  Unfortunately, there's very few ways for an unauthenticated user to interact with Appian.

Portals is one way, and I don't know if it would require additional licensing.

Another approach might be to have the "Approve" or "Reject" buttons configured to send emails.  The email address could be set to an Appian process model, which will kick off when it receives the email.

Another approach is to add a script in the HTML code to call a webAPI on Appian using a service account. Not a good one tho, but can work if there is a dead end. 

Thanks for sharing the details.

I am not sure if there is a way we can set an email address to trigger the Appian process model.

When I go through the documentation, it was saying

"If a single email contains links to multiple tasks, only the first task in the list of links can be completed".

But, in my case, I need to have 2 options/task, one for "Approve" and another one for "Reject".

Not whether it will fit to my scenario or not.

https://docs.appian.com/suite/help/22.1/Sending_an_Email_Message_to_a_Process.html  It looks like it's a bit complicated, and I have to say that I've never personally done it myself, though I have seen it work on projects I was on.

This is why the recommendation was not task links.  Also, this fails to meet your condition of users not having to log into Appian.  The process models can receive emails and start regardless of whether anyone logs in, in addition to some of the other suggestions presented.