For general discussion and questions, it is strongly recommended that you use the mailing list.
If you find bugs, please file them in the issue tracker.
The maintainer of Meson is Jussi Pakkanen. You should usually not contact him privately but rather use the channels listed above. However if such a need arises, he can be reached at gmail where his username is jpakkane (that is not a typo, the last letter is indeed e).