Judging by the IP 91.200.41.141 you have a boxed version of OneBox, you host it on your server.
According to the "box vs cloud" rules, the customer himself is responsible for his server, but we will try to help you, at least telling you "what to do".
Option 1.
It is most advisable for you to contact your hosting provider (hvosting), and ask/order from them what you are asking for.
Option 2.
OneBox Dev Production integrator
https://crm-onebox.com/en/integrators/ can do it too,
but, all the conditions, guarantees, etc. - this is already a question for them.
Also, you should understand that when you get into the spam database - this is not a "vulnerability", but rather the nuances of setting up a mail server.
I recommend using
http://mail-tester.com - send a letter to the specified mailbox from your OneBox, then mail-tester will show "what's wrong with your mail" (not OneBox, but mail).