Autodiscover
Every domain registered at IONOS automatically has the CNAME record autodiscover. This DNS record provides a mechanism that configures an email mailbox in an email program, such as Microsoft Outlook, only by entering the email address and password.
The setup process of email programs is simplified with CNAME record autodiscover, 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 IONOS. This can cause problems with certain email clients. For example, Outlook 2016 does not support manual setup of Exchange mailboxes. They can only be configured using autodiscover.