Wiktionary has a mailing list to discuss the project, although it is rather inactive. It can be useful for communication with Wiktionary projects in other languages. If you just want to ask a question, you should probably consider using the IRC channel; If the topic is about the English Wiktionary only, you are likely to get a better response from the appropriate discussion room.
Wiktionary mailing list
Mailing list for the Wiktionary project.