Mail::IMAPClient provides the ability to pass a pre-connected
Socket to it. We can rely on this functionality to use
IO::Socket::Socks in place whatever socket class
Mail::IMAPClient chooses to use.
The --proxy=s is shared with curl(1), though we only support
socks5h:// at the moment. Is there any need for SOCKS4 or SOCKS5
without name resolution? Tor .onions require socks5h:// for
name resolution and to prevent data leakage.