Gmail
From Leo's Notes
This page was last edited on 21 April 2020, at 17:39.
Troubleshooting
When trying to add an external email address to Gmail using SMTP (Port 465 with SSL), I got the following message:

Authentication failed. Please check your username/password. Server returned error: "Missed upload deadline (9.99s) (state CONNECTED_WITH_TLS), code: 0"
This happens intermittently and is not an issue with an incorrect password. The mail server is running cPanel.