My suggestion: don't use Nabble anymore if you want to interact with the Free Pascal and Lazarus mailing lists.
Yes, of course I will do.
But, imho, Nabble could warn its administators-users that it is no longer going to deal with mailing list.
I did not receive any warning (did Leledumbo receive one for nabble-fpc ?)
The other point is that the same happen with nabble forum and this is much more annoying because nabble-forum is not mirror but "original" one.
And I use for some projects nabble-forum.
All that to say: nice that you jumped into Gitlab, but even better, when all is ready, to have your own git server with your own fork of GitLab source.
Fre;D