This is not what i said ! You can do a very simple SQL query find there are a another website with the same domain so first come first served.
And no this is not better than a human but it's take less time and it's better when you haven't this option checked.
You can not add duplicate domains, so if customer a added domain1.tld as mail domain, customer 2 cannot add it. So if thats all you want, then its already implemented. But it wont solve the phising problems as these problems arise when someone adds a domain which is not used on your server but might be used by other customers to send email to.
This is not wat i said, i said that with a Regex+SQL you can see if a domain is already used IN YOU SERVER, and this is logic no ?
Although this is not what I said, yes there's a regex that it allows you to do this and it is extremely simple regex you can do it in 15 minutes (Okey the script need to download a whois page from a whois provider (XML: HTML or anything else) and you perse it using regex to find the name after this you use a condition and it's done) but this is not what i say to do, what i say to do is to simply check if a domain is already used by another clients if we haven't check the option of limited domain, yeah okey it's not betted than a human but it's fast the same
1) You can not access whois data from all domains with a script. E.g. a .de domain requires a captcha and some tld's hide the owner details.
2) The whois data does not always match the client data.
3) Domains can be rented, so the person in the whois is not the person allowed to use it.
So if you reject domains based on whois details, you will get a lot of customer complaints.