SRV record and CNAME flattening

I have a _client._smtp SRV record that points to the root domain. CNAME flattening adds some junk rather than returning this verbatim. Is this the expected behavior of this record? It seems like it either shouldn’t be, or should be documented as such.

dig srv _client._smtp.example.com
_client._smtp.example.com. 300	IN	SRV	1 1 1 _dc-srv.5e6364ad1fc6._client._smtp.example.com.

I don’t recall why this record was there in the first place, but migrated it as-is from my previous dns provider. Possible extraneous.

Are you running an SMTP server on your apex domain hostname?

Normally you would point an SMTP SRV record at a mailserver that uses a dedicated hostname that is not proxied through Cloudflare.

The prefix you see is created by Cloudflare synthesizing a hostname to accommodate protocols that are not compatible with your proxied record.

My apex domain is a CNAME to a github pages address.
My MX etc. all points at FastMail.

I think I found the culprit on this. DNSimple has this in their FastMail template. It’s not in the FastMail docs anywhere, and the closest thing I’ve found to anything relevant is an expired RFC draft-crocker-csv-csa-00, so I’m pretty ok with just removing this.

Yep, I understood what was happening, just was surprised that it happened.

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