For a mailbox hosted with us, open cPanel, Email Accounts, then Connect Devices. Use the Secure SSL/TLS Settings shown for that mailbox rather than copying another account's hostname.
Use your full email address as the username and your mailbox password. IMAP receives and synchronises mail, while SMTP sends it.
For secure IMAP, use port 993 with SSL/TLS. For secure SMTP, use port 465 with SSL/TLS and enable outgoing-server authentication using the same mailbox login. Use a different port or encryption combination only when it is explicitly shown in your account settings or confirmed by support.
Keep certificate validation enabled. A certificate warning, login error and delivery bounce are different problems, so note the exact error rather than changing several settings at once.
See Android email setup or creating a mailbox and finding its connection settings. Please send support a redacted screenshot if the app cannot connect, without your password.
