Incorrect Email Settings 1
Most scan to email issues stem from incorrect SMTP settings.
Incorrect DNS Settings 2
If using an SMTP hostname instead of an IP address, the device needs an external DNS to resolve the hostname.
Incorrect Gateway Settings 3
A gateway is needed to connect to an outside SMTP address.
Office 365: Certificate 4
Some MFPs require a certificate in order to use O365.
Gmail: Less Secure Apps is Disabled 5
Gmail started auomatically disabling Less Secure Apps on all email accounts. MFPs are considered Less Secure Apps and require this feature enabled in order to function.