Your last post you stated you don't want to have to create 50 distinct DNS zones.
1- you mean zone files as opposed to zones; a zone file pertains to a domain whereas a zone pertains to a hierarchical portion of a domain
2- the whole point of DNS is that a given DNS record pertains to a single domain name, and it cannot pertain to multiple domains. Each domain must have a zone file associated with it, otherwise there is no way of knowing on which web server that domain's data resides.
Therefore you have no choice but to create 50 DNS zones, regardless of whether you want them all to point to the same server (and / or the same site) or not. This is how the internet works.
Luck has it that your DNS zone file is probably created automatically and managed by either your domain registrar, a third party, or you (i.e. through ISPConfig).
Depending on what nameservers you have set for the domain with your registrar, (their own? your own server running ISPConfig? a third party?), you may also be lucky enough that the bulk creation or copying of zone files is supported, thus saving you - ooo - at least 30 minutes of your time in manual, repetitive, computing tasks.
And if you are really lucky, they may further provide you with the mechanism to redirect sites using something they may call "web forwarding", or similar. (ISPConfig does - as a previous poster mentioned.) This is nothing to do with DNS.
If you are even more lucky, they may allow you to set such redirections in bulk. (Hmmm, ISPConfig might not help you there.)
And if you are the luckiest person ever, if your domains' NS servers are with the registrar or a third party, they may do this without trying to track your web visitors' personal information! (Although I doubt it.)
Regarding trying to 'add an A record to receive a redirection', (i.e. adding an A record to your target site) there are too many things wrong with this statement to address here, but rest assured, what you are trying to do really will not work.
As for creating DNS records to 'redirect' your site (technically this isn't redirection, it's just pure addressing), well - don't waste your time. CNAMEs are designed for aliasing purposes and won't do what you require.
You will need to set the A records for each domain to point to your ISPConfig server. (This is either done at your domain registrar, or if you decided to host your own name servers - dumb idea unless you have at least 4 geographically separated servers of your own - then it's done within ISPConfig.)
Then in ISPConfig you will have to create 50 sites, because that's the only way of getting 50 virtual hosts each having its own host header for the given domain name for which you created an A record. Then on those 50 ISPConfig sites, you will need to set up redirection. And be glad you didn't have to write the redirection yourself
In conclusion, if you really want to take the SEO-suicidal step of redirecting 50 domain names to the content on one domain, then you should definitely consider doing this using HTTP redirection. Not just because this is the right way, but because nothing else will work.
Sorry if this post comes across as sarcastic or rude. I'm a sarcastic and rude person in real life, too. I hope to be informative, however.