Thanks, this set me on the right track to solve my problem. Port 2525 was needed to send emails out from a Linode server.
After that sending an email resulted in the following error
Error sending email! Error sending email: Failed to send email. Reason: 140261834299264:error:1408F10B:SSL routines:ssl3_get_record:wrong version number:…/deps/openssl/openssl/ssl/record/ssl3_record.c:332: . Please check your email settings and resend the invitation.
After some digging I found the following link explaining the problem
The problem is that when you use secureConnection=1 the mail system (in node.js?) seems to try to connect using SSLv3.
SSLv3 is a deprecated protocol that thats some vulnerabilities and is exposed to POODLE attack.
So nginx.conf is usually configured to disble SSLv3 protocol and thus the error.
Instead of configuring nginx to use SSLv3 and opening up my server to a vulnerability, I just changed secureConnection to false instead of secure.
The follow link explains why that works.
Thanks for the reply. It pushed me in the right direction. I never thought that Linode would block the default port.