What is the use of message queue?

I recently wrote a website that needs to constantly poll an interface. If the data changes, I need to send an email. Now some people say that I can’t receive emails during the day and can only receive them at night. I guess it’s because I send emails during the day. The frequency is too high so some emails cannot be sent? Do I need to use message queue in this case? (I am writing a backend in PHP. I wonder if SF allows me to post the URL of my website. I am afraid that the administrator will think it is an advertisement...)
In addition, what is the relationship between message middleware and message queue?