Max. number of email white / blacklist entries

No. But maybe you have assigned that customer to a reseller and you are hitting the limits of that reseller account.

 

Check if the client is set to custom limits.

 

On the client limits page near the top of the page.

 

Yes; if they have custom limits you will need to change the limit for that client individually; alternately, assign a limit template to the client and those limits will apply.

 

Does the client belong to a reseller? Check the reseller's limits if so.

 

Sorry, in rereading this thread I see you already answered that.

No idea at this point, I'll try to test that limit when I can, I suppose it's possible there is some bug affecting that and no-one has run in to it previously.

 

Just tested the latest code (dev version as of yesterday) and there is no problem here. I tested a client with Custom limits, and it respects exactly what you set for the limit. Maybe you have an outdated code version? (I don't remember any recent bugs along those lines, so maybe *very* outdated?)

 

You should have really mentioned that you were not using ISPConfig.

 

I have never dug into the rounding plugin code much, so have no idea. I would post a question to the author (in GitHub, iirc).