CRM - Object address not found on party or party is marked as non-emailable

When you want to send an email using CRM, you may use direct method to send email or you may use SendEmailFromTemplateRequest. And sometimes you may get the error "Object address not found on party or party is marked as non-emailable". Once you debug and found the error, you will be differently know that either the email address of 'To' is blank or marked as 'No Email' or 'No Bulk Email'. But when if fields are set correctly, and if you get the same error, once shall we do?

Other than the To Address, you have to check the 'From' users email validity as well(which we usually forget to set), because if it is missing, you will get the same error 'Object address not found on party or party is marked as non-emailable'

And what will happen if the From field is blank? Then CRM conside From user as execution context user. (May be plugin executer in Plugin Context or executer in CRM Async Service for workflows or the credentials you used to communicate with CRM Service.) And if the email address of this user is missing, you will get the same error. "Object address not found on party or party is marked as non-emailable"