Today I am really annoyed at #GandiNet: I cannot send email through an *authenticated* SMTP connection because the IP address of my gateway (mobile network connection) is listed by SpamHaus. This is just unbelievable. They even have a doc page that just suggest to sort it out with SpamHaus 
@blmt The issue here is *which* list you are on. XBL is a policy blocking list. Their (Ghandinet) policy is to not accept mail from enduser devices directly. If you want to mail them, you have to use a proper mailserver, not something running at home on your private internet-connection. Use the smartrelay your ISP provides or become a RIPE LIR, request your own address space, properly manage it, and run your own mailserver like a proper ISP.
@burne to clarify: #GandiNet is my mail server (I still have a mailbox there :-/) and it is refusing to process my messages (that are directed elsewhere). Their workaround is to use their webmail..

@blmt To clarify: XBL is a policy list.

Your issue is not XBL or spam blocking in general. Your issue is the maintainer of the Ghandinet mailserver. It is HIS choice and his choice only to use XBL.

@burne indeed whose are the people I am annoyed at :)