How to Determine the Optimal Number of Messenger Workers in Mautic for Maximum SMTP Sending Speed Without Overloading the Server?

Your software
My Mautic version is: 5.0.4
My PHP version is: 8.1

Your problem
My problem is:To increase SMTP email sending speed, we configured the queue system and started multiple Messenger workers using the following command:
sudo -u www-data bash -c ‘cd /var/www/html/mautic && for i in {1..5}; do php bin/console messenger:consume -vv email --memory-limit=512M --no-reset > var/logs/worker_$i.log 2>&1 & done’

This runs 5 parallel workers, which significantly improves sending speed.

However, the main question is:

How do we determine the maximum number of workers we can safely run without overloading the server or SMTP provider?

Steps I have tried to fix the problem: