question

I would guess that with the merge, there were several different user extensions that were using the same "Email addresses permitted to send faxes".  You can easily check this by removing, saving, and then re-adding the email address(es) back in as permitted.  You will get an error message immediately if the email address(es) is on a different user extension.

Also note that the user's email address cannot be used on any other RC user account as a permitted email to fax from - in any RC account, not just the ones you are using.  This is not a great verification system, in that anyone could setup any email in their fax permitted list and it is now locked from anyone (even the legitimate owner of the email) using it on a different account.

This may also be the problem, as you indicated, that your email addresses are still assigned as permitted fax senders on the old user extensions.

We need an RC improvement to this function by:
1) adding an email-verification process (ie. send a verification email from RC to any email that is added as a permitted fax email, and it would include a button to press to verify the owner wants to be able to send emails from their email account)
2) when adding a permitted email and the error message is displayed that this email is already used by another RC user extension, then some RC user-extension-account info should also be displayed indicating where the email address is currently being used

Thanks, Michel, for lending a hand on this one. 

Shanell, if you're not having any luck, please reach out to us at Community.Support@RingCentral.com and we'll have someone reach to help to get this issue sorted.