Please tell me how to send files from a request to an email?

I can create the letters themselves, containing the description and other text from the request, but I don't understand how to get a list of attached files in the request and include them in the letter.

That is, there is a request, in addition to the descriptive part, there are attachments. The number of attached files is unknown, it can be zero, it can be 1, etc.

And now all of them from the request need to be attached to the letter and sent. How to do this?

Thanks