Once a new user has been registered on the system, the user would typically receive a welcome email containing their login details for the Proofpoint Essentials Interface.
If they have not received a welcome email it may be because your default new user privilege is set to silent user. Default new user privileges can be found under Company Settings > Import users or SMTP Discovery.
In addition, if users were set as silent, you can use the mass update feature to set these users to end-user. In addition, at the same time you can use the feature to "Send Welcome Email" at the time of update.
The Proofpoint IPs, per the Lockdown set-up portion, do not need to be added. Adding the IPs assist in recognizing the Proofpoint Essentials servers to not be blocked by any of your other security products.