Even if some one try to configure connected system or integration then it should be blocked there itself.
Basically we are trying to stop accessing external sites/services to fetch the data via Appian in general.
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This is relatively easy to do for on premise installation.
For Cloud, I've never heard of outbound restrictions. I would suggest you inquire with Appian Support about this.
What could be the way for on premise installation? Any pointer on documentation on this?
Tons of ways to do this. Easiest way is just to configure the firewall on the server that has the Appian application server. You'll have to safelist all the IPs that you want to allow.
Thanks