A few years ago we transferred one domain from Google Domains (yeah, it was still running!) to Namesilo. After we configured nameservers correctly pointing to IONOS which was holding back then the MX records, sometimes e-mails got to their destination and sometimes not, even e-mails from the same domain. It was driving us mad.
Long story short: DS records migrated from the old registrar were not deleted and DNSSEC is not allowed on Namesilo’s default nameservers. So if you ever have a similar trouble be sure to check out the DS records, which are not visible right away; Then just wait 24-48 hours and it should be working fine. Google being Google, but that is another story 🙂
