BTW: sorry for the somewhat wierd looking thread. I forgot to manually include haproxy@formilux.org as recipient and manually re-sent it afterwards to the list - for the sake of completeness.
And I am forced to use this abomination of a mail reader called google mail, because my mail relay at 1und1.de won't deliver mails to the formilux.orgmail server. It complains with: A message that you sent could not be delivered to one or more of its recipients. The following addresses failed: <haproxy@formilux.org> domain name system error: host mail.formilux.org: mail exchanger has no ip addresses Which is not entirely true, but mail.formilux,org is a CNAME instead of an A record and maybe the 1und1 server is complaining about that.
