My experience of this is that is because Cura over extrudes the walls deliberately to help adhesion and strength - I want to say the setting is called “overlap”. It’s the one where the infil runs into the walls a little bit to tie together the edges, but that’s always going to result in a bit more plastic being laid down in those areas.
Normally it causes a bit of a brim to cut off, but in your case it might just be enough to let it stick round the brim but nowhere else.








Do you have any experience with Docker? I’ve been running a mail server myself without too much trouble. More than happy to help if you wanted similar.