I try to send an email via smtp but I get an error from nginx Server Error (500).

if I run the site on a local machine, then the letters go away, but the server fails.

result from command netstat -ntlp | grep LISTEN

tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 20380/nginx: master
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN 2702/systemd-resolv
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 957/sshd
tcp6 0 0 :::22 :::* LISTEN 957/sshd

I set up the server manual which indicated the following settings https://gist.github.com/postrational/5747293#file-hello-nginxconf

I also tried to open the port through the command, but this did not help.
iptables -A OUTPUT -p tcp -d <myIPdroplet> –dport 587 -j ACCEPT

can someone help me with the problem?