Install Email On Ubuntu
This is just a summary on how to install mail server on Ubuntu. You can check really complete tutorial from Digital Ocean blog right here How Install Postfix on Ubuntu 18.04, it's very nice tutorial, you can just follow there for more specific explanation, because this post is not gonna explain it in detail.
1. You can use Postfix
sudo apt install postfix
2. Configure Postfix, leave the default value, basiccaly you just press enter
sudo dpkg-reconfigure postfix
3. Install s-nail
sudo apt-get install s-nail
4. Go to your domain manager, on mail section select type MXE record and set the value to your server IP.
5. Set /etc/hostname to what you want to make something that would be your email hostname, for example yourusername@hostname.com
6. To test your email is working or not, you can doing like
mail -s "Subject" your-gmail@gmail.com
Please refer to digital ocean blog on the link above for more detail.