Hi Sterp,
sorry if I am a bit nit-picking. You wrote:
I have tried to delete…
Deleting doesn't work for You? Deleting is a two-step-process in BwPostman: First archive the item (subscriber, mailing list, newsletter,…), then change to archive and there You are able to delete the items.
And You are right: Only mail address is checked creating a new subscriber. You may check this with a new subscriber, i.e.
Søren with mail address zzz@yyy. dk. If this also fails, then You definitely have a subscriber with this mail address. If You can't find this mail address in BwPostman, then please have a look to the table #__bwpostman_subscribers via phpMyAdmin.
BR
Romana