Email wont send

Hi i Have just had a problem with emailing invoices, it has been working fine for years but suddenly giving an error ‘’ The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required. ‘’
can anyone help with this please

Read the Guide: Troubleshoot email issues | Manager. Follow all relevant links, take all recommended action. If you still cannot resolve your issue, provide all requested information.