Email Settings Design Preview results in Internal Error and Templates are not applied

[lcduong]

This PR related to this issue #285

• Fix issue got internal error when preview email template
• Fix issue when sending mail using sendgrid, mail template not applied

Summary by Sourcery

Fix internal error during email template preview and ensure templates are applied correctly when using SendGrid. Improve error handling and logging for email template parsing.

Bug Fixes:

• Fix internal error when previewing email templates.
• Ensure email templates are correctly applied when sending emails using SendGrid.

Enhancements:

• Improve error handling and logging when parsing email templates.