GD Mail Queue Pro 5.3 is a smaller scope release mostly focused on the SendGrid REST API support and a first step in changing system requirements and preparing things for some new upcoming features.
SendGrid REST API support is built into the plugin core, and it uses the official SendGrid PHP library. The new plugin version includes an updated library (version 7.9.2), and it also improves how the emails are processed for SendGrid. This includes few improvements related to the email preparation and full error handling during this stage where SendGrid runs some email address related checks. This also fixes the error thrown when validation fails, breaking the queue processing for invalid email addresses.
This version addresses more things, including some additional bugs, and it now also shows how long is the timeout for script execution is set for PHP.
The work will soon begin on the major update to the email sending that will use global limits for all emails and queues.