Email Validation Fix on Ubuntu Server

My website, https://nextgtool.com/, hosted on an Ubuntu server, is experiencing issues with email validation. This problem needs a swift resolution.

Key Requirements:
- Troubleshoot and fix email validation issues
- Ensure the website operates normally post-fix

Ideal Skills:
- Proficient in Ubuntu server management
- Experienced in website troubleshooting and email validation systems
- Capable of understanding and implementing instructions from provided documentation: https://ommune.com/mailtidy-documentation/worker-setup.html

Please note, I do not have a specific email provider, and the issue appears to be affecting all users. It has been ongoing for more than a week.