Send Email Configure From Address

You no longer need to create custom files to achieve this. Please refer to the following link: https://docs.appian.com/suite/help/19.2/Configuring_Custom_Email_Senders.html

Got it confirmed below are the 2 files that needs to be updated for  version above 18.4

APPIAN_HOME\deployment\web.war\WEB-INF\conf\process\email-address-config.xml

APPIAN_HOME\deployment\web.war\WEB-INF\resources\text\jsp\WEB-INF\conf\process\email-address-config_en_US.properties

I would strongly suggest against changing those files if you are in 18.4 or later. As Tejas mentioned above, there is a new feature that allows you to directly type in the sender email address into the send email node, which is much easier to manage (and you can even use an expression to define the sender email). Using the files you mentioned requires (1) updating custom.properties (which you need access to the server to update), and (2) restarting the application server, which could be disruptive to your users.

using the existing functionality the email send out has "on behalf of". which our client do not want to see and they wanted to reply back to the same email for further actions. 

Is there any way to get off "on behalf of" please let know we are looking for that solution only

I previously asked Appian support about this and they claimed it was implemented that way due to "security requirements" or some-such; i found this to cause the feature to be basically unusable for my main client as well because it causes emails to bounce for various reasons.

Note that the 17.1 Custom Email Senders documentation you linked to above, will also come out as "on behalf of".  The reply is returned to the correct "From" setting however.  We've been using this internally for years, in the process of converting to the new in-node configuration as Tejas linked to. 

However there's a specific difference with the new functionality that's impossible to override.  It boils down to the fact that the "sender" header or similar (i'll have to look again to remember if this is the correct one or not), is forced to use the environment-specific "admin email address" when sending using the new setup.  The prior custom sender workaround which we've also been using for 5 years in production, allows emails to be sent as if they're actually coming from the user account passed in.  In our system this caused immediate failures because at least one of the mail handlers along the line rejected the apparent mismatch.  If you examine the headers for the new way compared to the old way, it'll become immediately obvious what the difference is - and no resolution has been provided for this (again, "because security" or something.)

Interesting, in our environment the header information as well as "on behalf of" is the same across both old and new configuration methods.  Just ran a test and compared headers, they match.. 

I'm wondering if your environment had the sender property modified in the email-address-config.xml file.  We've always used the server email sender "bpm" in there, with the "From" as the address to be included "on behalf of".

   <address name="serviceDesk" sender="bpm">
     <expression>=cons!SERVICE_DESK_EMAIL</expression>
   </address>

Ah okay that is good to know - I wasn't aware of this issue with the new custom email sender, and I'll add to the case to address this scenario. Thanks for the info!