Mailster SendGrid Integration

This Plugin requires Mailster Newsletter Plugin for WordPress

1. Upload the entire mailster-sendgrid folder to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Go to Settings => Newsletter => Delivery and select the SendGrid tab
4. Enter your credentials
5. Send a testmail

• fixed: issue with invalid data type with WP 5.5

• fixed: issue with Mailster 2.3.16+ and reply_to headers

• fixed: undefined reply_to email address

• switch to SendGrid API v3 requires now an API Key
• embedded images works now with the WEB API
• several improvements

• fixed: issue with slashes in content when using the WEB API

• initial release