6.0.0 Patient Portal SMTP Email error

I am new to OpenEMR. Installed version 6.0.0 plus patch#1, locally hosted in Ubuntu 20.
When testing the Patient Portal, I get EMAIL ERROR: SMTP connect failed.
The new patient records are created, but no notification email is sent.
I performed a test of TCP Port 25 (smtp) access with telnet, from the OpenEMR Ubuntu server to the SMTP server, and could received the test email. The corresponding SMTP parameters are set in Administration->Globals->Notifications. Please HELP!