If your website is not through a premium email provider (like Google’s G Suite) it is likely you are on a shared email server through your host. There is no real “fix” for this issue other than changing your email provider.
Depending on your email provider, you might need to check with your host or individual provider (like Google G Suite) to troubleshoot the issue. Refer to your Technical Support contact.
Try updating your plugins. Check for conflicts between the plugin and your current version of WordPress. Check with your Technical Support contact.
Your license might not be connected, or could have expired. Check with your Software Updates, Billing, and/or Technical Support contact to investigate the issue.