As of the 2020.07.26 build (and later) of AssetCloud On-Premise and InventoryCloud On-Premise, an SMTP server is no longer necessary in order to add additional users to the system. Note: To enable email features such as sending reports, notifications, etc., valid SMTP server settings must be entered.

Process to add user(s) without an SMTP server:

One-time configuration: At the upper right, click the gear icon, then Settings, then Email. In the section "User Registration Without SMTP", check the box "Register users without SMTP." Click the Save button at the bottom.

AssetCloud: At the left menu, click Users, User, then the New button.
InventoryCloud: At the left menu, click Manage, Users, then the New button.

Fill out at least the required fields (First name, last name, email address, role), then click the "Add & Invite" button at the bottom.

The profile completion screen appears. Specify at least the username and password here, then click the Done button. The screen returns to the login prompt.

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For earlier releases of the Cloud On-Premise products, adding new users requires an SMTP server on the same network as the OP server (just like with the web edition).