Hope you are doing good. Port 25 is blocked on Google Compute Engine and Vultr hosted servers. Secondly, TLS and SSL connection depends upon your SMTP provider. Cloudways works fine with all 25(except GCE and Vultr), 587,465, 2525. You can easily check which port your external SMTP host is allowing using the following steps .
1) Connect your server via SSH
2) telnet smtp.provider.com
e.g telnet smtp.gmail.com 587
If it is showing you 220 response, it means that host allows connection on that port. You can simply use that port in SMTP plugin or SMTP addon.
P.S enter quit at the end of telnet command otherwise it will not close the telnet session