In order to obtain the TSL certificate ?
Please stop spamming the forum … whether your question is asked once or four times will not change how quickly it is responded to. Actually, it will delay the response.
Please read the existing posts on the forum as all of your questions have already been answered multiple times in the past few days/weeks.
Please give up the idea of hosting ‘email mailboxes for people who have their own domain names’. It is a complex matter which in your own words you are a ‘total beginner in this’ and most likely are setting yourself up for failure.
Please don’t ask the project maintainer to assist you with an unsupported modification as it is unsupported.
What it appears that you want to do is outside of the scope of Mail-in-a-Box. I suggest that you find a company which deals with white label email reselling. There is one in CZ which looks very promising and affordable. I do not know if promoting them publicly on this forum is permissible so feel free to PM me for details.
And lastly, @joshdata suggests that I have to chill … if my replies seem harsh to you, they really are not meant to be. So my apologies if you were offended by my reply or tone.