There is a mailing list devoted to GNU Pascal. You can write to the mailing list, e.g. if you have problems installing GPC or if you found a problem with GPC (please see Reporting Bugs). You can also use it to discuss suggestions for improving GPC and, most welcome, to offer your help or contribute code, documentation or other work. Mails to the list should be in English.
When you are subscribed to the mailing list, you can send a message to the mailing list by sending email to the list address email@example.com as if it were a person.
To leave the mailing list, you can use the same form as used for subscribing.
You can reach a human moderator at firstname.lastname@example.org.
There is a separate mailing list for discussions about GPC documentation, email@example.com.
There is also a (low-traffic) announce list, firstname.lastname@example.org that you can subscribe to stay up-to-date.
If you like to announce a contribution, a service or an event related to GPC, you are invited to post to this list rather than email@example.com, but please don't use the announce list for questions or discussions. Please note that all mail sent to the announce list is forwarded to the regular list, so you won't have to subscribe to both lists if you don't want to miss anything. For the same reason, please don't cross-post to both lists.
There is also a German speaking mailing list, firstname.lastname@example.org (note the hints above).