You can clone with
HTTPS or Subversion.
When trying to recieve mails on this server from GMail, I get a 502 not implemented. It's unclear which command is causing it (as the NDR does not note it), but it seems that many of the commands on the following page throw that error:
I debugged this issue. GMail doesn't accept a status-code without a domain name. A simple workaround is to put your domain name into your ack.accept function.