Than you already know the drill and depending on your scenario and recipients pick the correct option
https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/how-to-set-up-a-multifunction-device-or-application-to-send-email-using-microsoft-365-or-office-365
Powershell via Send-MailMessage is your friend while simulating the mailflow
https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/send-mailmessage
If device firmware does not support TLS 1.2
and no newer firmware is available for your MFC device then
- pick either a newer device or
- lower tenant settings via Exchange admin center > Settings > Mail flow > Security > 'Turn on use of legacy TLS clients'
❗ But be aware that this impacts the subscription and should be used as a last resort (if at all).
Regards