Issue Summary

Currently, 'Send Customized Email' only supports a payload of up to 256 KB. This is not sufficient, if we have to add HTML content - such as a base64 inline image. We would need to have a higher limit to support different scenarios.

Steps to Reproduce

1. Create an Automation Rule with a 'Send Customized Email' action included in it. 
2. Add more contents in the action such that the payload weighs more than 256 KB. An easier way to do this is to add a base64 inline image. 
3. Execute the rule.

Expected Results

Email should be sent.

Actual Results

Email action fails with this error:

Failed to send email. 

Workaround

A workaround for adding attachments to the email is to upload the attachment in web (or a file server) and use HTML Hypertext Reference (href) function to add the attachment to the template.