You would naively think that if the operator of MailCow has to manually insert DNS records to his domain fully outside of MailCow, he would find a prominent sentence in the Docs such as:
“The blue DNS button is for reference only. You have to manually put the records shown into your DNS server, else nothing will work.”
Instead there are 3 lines of vague blabla in the place in mailcow where people expect actionable HELP/USAGE text.
Note that in Mail-In-A-Box that DNS business is done automagically, not a single click required.