It's possible. I will first write what you want, to make sure I got everything right, and then I will explain how to set it up.

WHAT YOU WANT
- ATA for outgoing faxes. Should present the main fax number as caller ID.
- also sending outgoing faxes through the app or using email-to-fax. Should present the main fax number as caller ID in these cases as well.
- Incoming faxes are received to one or several email addresses.


HOW TO DO IT

• ATA
  set up a new user for the ATA. Set the fax number as outbound caller id for calls and faxes. there should be a step-by-step on how to set up an ATA if you search the support page or google sth like "ATA ringcentral"
  
  
• NON-ATA
  - go to phone system>Phone numbers > All numbers and click on the fax number. Make sure it is assigned to the "Operator extension".
  - Check who the operator extension is in Phone system > Auto receptionist > General Settings > Company Call Handling > Scroll down and look for Company Fax/SMS Recipient
  - Go to Users and click on the ext. that is the Company Fax Recipient. Go to notifications>switch to advanced settings>customize notifications for Received fax. Uncheck "Use same email as voicemail" and add the email addresses which should receive an email whenever a fax is received.
  Include attachment with email
  
  
  
  In case you want something slightly different than what I described, it's probably possible. Just ask here and I'll try to help.
  
  
  
  

I'm always impressed with your suggestions @Welcome 01! (clap emoji)