add mail by text file and also html customization

[therealelyayo]

Feature Request: Mail Functionality with Text File and HTML Customization
Overview:
Currently, our application supports sending emails programmatically through various methods. To enhance usability and customization options, we propose extending the email functionality to allow users to send emails by providing content via text files and customize the email layout using HTML templates.

Use Cases:

Use Case 1:
Users may have predefined email content stored as text files (e.g., .txt, .md) that they want to send as emails without reformatting.
Use Case 2:
Users want to customize the structure and styling of the email using HTML, including headers, footers, and CSS.

Proposed Features:

Email Content from Text File:

Introduce a new method or API endpoint that accepts a path to a text file containing email content, including subject, body, and attachments.
Support common text file formats such as plain text and Markdown for email content.
HTML Customization:

Provide options to customize the email's HTML structure and appearance:
Allow users to upload or reference HTML files/templates for email layout.
Support placeholders or variables in the HTML templates that can be dynamically replaced with content from the text file.
Integration with Existing Functionality:

Ensure seamless integration with existing email sending mechanisms (e.g., SMTP, API endpoints).
Document clear usage examples and provide SDKs or libraries for popular programming languages to facilitate implementation.
### Security and Validation:

Implement security measures to handle user-provided content securely, preventing vulnerabilities like injection attacks.
Validate input to ensure compatibility with email standards and prevent malformed content.
Benefits:
Enhanced Flexibility: Users can leverage pre-existing text files and HTML templates, reducing duplication and streamlining email creation.
Improved Branding and Personalization: Customizable HTML templates enable consistent branding and personalized customer communication.
Implementation Considerations:
Performance Optimization: Efficiently handle text file parsing and HTML rendering, especially in scenarios involving large volumes of emails.
User Experience: Provide intuitive interfaces or command-line tools for configuring email content and HTML templates.
Example Usage Scenario:
Demonstrate a typical scenario where a user might upload a text file containing an email draft and use an HTML template to format the email's appearance, showcasing the feature's practical application.
Additional Notes:
Include any additional requirements or constraints specific to your application or platform.
Reference any similar features in competitor products or community requests to justify the feature's implementation.