The important thing to understand about Mixolydian, is if you don't understand the Mode in use over its backing tracks, chances are you're just using it as an Extension of the Major scale in function.

You can solo all day over what you think is one thing but functionally its doing something else entirely different.

To say use it over a Dominant 7th is really only partly answering the question. Isn't it? There are a multitude of uses for the Mixolydian mode, but you do need a foundation in Music Theory, to where you understand triads and their functions within the Key, Knowledge of extended chords off triads, and the understanding of the interrelationships with Chords and their Scales.

I'm not trying to double talk anyone here, but the competent knowledge of Modes is something that requires you to know your basics in music theory, and it's a fact that's rarely discussed adequately out there. For instance, in Dorian, the characteristic note is a Natural 6th. The more instances of chords which use the diatonic version of that mode and incorporate the Natural 6th, the more cognizant that Mode application will be. Also you have to structure your notes so that it the tonal center is in fact the root of whatever Dorian scale you are playing, for it truly to have a Modal feel. Hence many people use 2 chord vamps or pedal tones, or say listen to Miles Davis' So What to get an understanding of Dorian, for example.

The truth is, you'll need quite a background in applied music theory to ever fully answer your questions beyond the answer, given and that's not always what someone wants to hear.

What's left, is for you is to decide how meaningful to you is it to to have that level of knowledge.