Wouter suggested ACL filtering for my exim4 hostlists problem. However, my original plan was to get the data size announced in the emstp headers. For that, I need to set message_size_limit during connection establishing. And for that, host lists don't work.

Using something in the data acl violates my sense of beauty. If it is possible to announce it at the start of a message, I want to do that and not do it way later in some ACL.

Of course, I might still be forced to come back to that suggestion, as I need it for my buildds pretty soon. Thanks, Wouter, for your help.