I have been trying for 2 weeks to get our issue resolved with "customer support". We had several individual accounts/fax lines combined into a single account, keeping all the numbers the same. Now when one of our users try to send a fax via email, we get a return message that there are too many mailboxes and to log in to the account you are not using and delete your email address there. It seems like their system is still seeing the info from the old accounts and confusing it with the new account. Every call or chat to support always starts back at square one, describing the problem, sending screen shots, etc. and getting no where.
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