@Julius Not very sure about the issue. As per the error, it seems the Port 465 is blocked on your server where Wordpress is installed.
In case you have the shell access, then try doing telnet and check whether the outgoing smtp port over 465 is opened or not.
Else, you can also try connecting over Port 2525, which most of the time works. Not sure, if zoho SMTP supports port 2525 or not.
In case not, you can try using Pepipost SMTP, which works on port 25, 587 and 2525.
25000 emails per month is Free for lifetime and no charge for email opens.
Pepipost Wordpress Plugin for reference:
https://wordpress.org/plugins/pepipost/