Google Summer of Code FAQs
Q: How should I prepare for Google Summer of Code?
A: Google Summer of Code needs you to interact with the community and familiarize yourself with the codebase of the software. The best way to do this to set up a development environment locally. Try not using an automated process (if any exits for the particular software you want to work on). After that visit the bug-tracker of the software and try finding a bug that suits you. It may be a little difficult to find your first bug, search for tags like beginner-friendly or easy or something like that. For mailman filter the bugs with easy and mailman3 tags.
Q: I have a doubt, now what should I do?
A: Its good to have doubts, but be sure that you yourself read extensively before asking one of the mentors or posting to developers list. I have told students time and again that, most of the answers are in the wiki or documentation of the respective projects, look into it yourself before asking. If you still don't find an answer, you can ask your mentors using the communication channels mentioned on their ideas page. Very often you don't get response on IRC instantaneously, try to be patient. Also you'd have answers faster if you collect a small set of doubts and send in an email to developers list, most of the mailman developers don't hang out much on IRC, or are too busy to reply there.
Q: Should I email one of the mentors personally?
A: Its generally not a very good idea, unless he/she expects you to. Ideas page of mailman does have email addresses of all the mentors, but it is encouraged that you send emails to entire developers list. If a mentor is interested to help you out, they'd simply reply to your post. Having said that, if you strongly feel like sending a personal query to one of the mentors, you should go ahead and do that.