Unifi Controller - Failed to send email for unknown reasons

I was recently trying to set up email alerts for the Unifi Controller but kept running into the error: Failed to send email for unknown reasons.

The problem seems to relate to an incompatible use of TLS/SSL. I've found two ways to resolve this problem:

• Connecting to the mail server using port 587 but disabling the option 'Enable SSL'.
• Connecting to the mail server using port 465 and enabling the option 'Enable SSL'.

From testing both methods above will send email alerts over a secured connection.