Domains registered before January 2022 may still have the CNAME record _domainconnect.1and1.com assigned. However, there is no difference in functionality between the records _domainconnect.1and1.com and _domainconnect.ionos.com.
This DNS record simplifies the connection between a domain at IONOS and an external website, externally hosted service, or e-shop provider via the Domain Connect protocol. The protocol is an open standard which allows an automatic connection between a domain and an external website.
The record _domainconnect has no adverse effect on your other existing DNS settings. You can use other CNAME records at any time. However, if you wish to continue using this automatic connection service in the future, we recommend that you keep it in your DNS records.