So i created a server (ubuntu) with nginx on it link to the tutorial i followed. I have multiple server blocks for my domain names and everything works perfect. But now i want to sent mail trough a php contact form but i get a 504 error (the code works I tested it on my hostgator server). So I looked if i had Postfix by sudo apt-get install mailutils and it says: mailutils is already the newest version.

So what should i do now