Hmm, seems that sylpheed recently started doing something strange when it sends messages, leaving either spider@localhost.localdomain or @darkmere.darkmere as one of the originating places on the SMTP path.
This is of course valid, for my local network where "darkmere" -is- a valid domain, resolves nicely and has a registered MX and so on and so on.
However, hosts on the net dislike this.
Well, it has made me work with evilution some more, and even though its evil and polluting (reply doesn't do reply-to-list if/when it detects a list folder, I can't associate folders with outgoing addressess, it doesn't import my adressbook, it doesn't autopopulate my addresslist either... *grr*)