We’re migrating our entire system from domain domain1.com to sub.domain2.com. The domain domain2.com is under control of a 3rd party, so in order to continue using certain Cloudflare services such as Workers, we configured a CNAME setup for domains *.sub.domain2.com. Now we need to setup some MX and TXT records e.g. sub.domain2.com but it seems that when using CNAME setup, we can only create CNAME and A records in Cloudflare. We asked the 3rd party to setup those records on their side but turns out it is also impossible since there is a CNAME record (for CNAME setup) for that domain already.
Please provide some information on how to proceed or whether a setup we’re trying to achieve is possible at all.
With a CNAME setup Cloudflare specifically does not control your nameservers, so you’ll have to configure MX records wherever your DNS is controlled.
As far as CNAMEs are concerned, yes, a CNAME does not play nicely along with other records, which is why you can’t set it up on a naked domain as well for example. However that’s not really a Cloudflare related issue and best discussed with your DNS provider.
Some DNS providers have an unofficial ANAME type which is not a CNAME but works similarly to it, maybe yours offers that as well, but that’s still something you need to clarify with them. Not being your authoritative nameserver, Cloudflare can’t do anything here. You’d need to switch to a proper Cloudflare setup to fix this on Cloudflare’s side.