Question:

My Deskpro On-Premise installation can't connect to my POP3 server, although the account details are definitely correct and the server log seems like the connection is being accepted.

When I test the account I get the error:

There was an error while trying to connect to the server. Make sure the host and port you specified is correct.

RuntimeException::0 cannot connect to host; error = Permission denied (errno = 13)

Answer:

The permission denied error can sometimes mean SELinux is preventing networking connections.

Run this command as root to enable networking from PHP:

setsebool httpd_can_network_connect=1