How to fix AT&T error code 475? Whenever you try to send the emails and you find an error that the message couldn’t be delivered, then it is what constitutes for AT&T error code 475. It can be a really common error and can be fixed quite easily.  Install new updates in the operating system and update the device drivers.  Send emails without any attachment or hyperlinks.  Delete the web browser’s history, cookies, and cache.  Sometimes the emails are not sent due to poor network connectivity.  Update the web browser or use a different one. If nothing works, then get in touch with AT&T customer care service for further assistance. Visit: https://www.customercarenumber-usa.com/att-customer-service/