This article provides the cause and solution when a user is unable to send outbound fax from their email and instead receives a notification error message saying the request could not be processed due to an "Unauthorized sending email address" as shown below:
The "Unauthorized sending email address" error message indicates that the email address from which the email-to-fax request was sent is not registered with FaxMaker Online. This is often an indication that the sender is associated with a FaxMaker Online subscription that has since expired.
It is mandatory for the origin email address to be added as a valid sender as GFI FaxMaker Online only processes emails received from email addresses specified in the Sending email field under the Faxing Settings dialog in the FaxMaker Online Administrator Portal.
Refer to Adding Users in the FaxMaker Online Portal for information on how the affected user can be added as a user allowed to send faxes. Renewing your FaxMaker Online Subscription describes how to renew expired subscriptions.
If the affected user has multiple email accounts, ensure that they are initiating the email-to-fax request from the account which is registered on the FaxMaker Online portal.
See FaxMaker Online Error String Explanations for a comprehensive listing of error messages that users can encounter while sending faxes through FaxMaker Online.