I installed and configured WP Mail SMTP and successfully sent (and received) a test email from the plugin. I then tried to add a new user to the site, but no confirmation email arrived nor is there anything in the sent folder of the email account. I set the plugin to "Use the PHP mail() function to send emails", I re-registered and the email arrived but not from the SMTP server.
I'm using SSL, port 465 to connect to smtp.zoho.com but as I said, the test email worked. Also note, that I am using multi-site wordpress, but this plugin is only activated on the sites, not the network.