I'm only slightly introverted, or was, now I'm a lot more social. Here is my experience, it might work for you too.
If I have a few questions for a user, sometimes rather than sending an email I will invite one of the people who depend on my work to come sit with me at my cube to go over the questions. I let them see what I am doing, discuss some of the changes, even let them see me make some of the changes while asking for their input.
Me: "So would you prefer it to tab from this field to that field, and not to that button over there like it has been?"
Coworker: "Oh yes!, can you do that to the other screen too? that always messes me up".
This can be very empowering to them, exciting to see it in action, and appreciative that you have let them have a peek in at and participate in the secret world that has so much influence on their day to day work.
Do this over time and you end up getting to know your co-workers, what they know, how they work, and maybe even make some friends.