All domains registered with 1&1 IONOS automatically have a autodiscover CNAME record. This DNS record provides a mechanism which configures an email mailbox in an email program, e.g. Microsoft Outlook, by entering only the email address and password.
The setup process of email programs is simplified with an autodiscover CNAME record, resulting in a significantly better user experience. You do not need to enter an email server name or port number, as this information is automatically passed through the CNAME autodiscover record. No manual setup is necessary.
We recommend that you do not delete this CNAME record, otherwise your domain will no longer support the autodiscover mechanism at 1&1 IONOS. This can cause problems with certain email clients. For example, Outlook 2016 does not support manual setup of Exchange mailboxes. Configuration is only possible via autodiscover.