custom-domain.upmind.app has no MX records.
Question and response
Question
dig custom-domain.upmind.app. MX
Answer
The response has no answer records.
Authority
upmind.app. 1800 SOA adi.ns.cloudflare.com. dns.cloudflare.com. 2397937331 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0