DANE is a standard that allows TLS certificates to be bound to DNS names using DNSSEC. As of today (2017), one of its most prominent uses is for email; bringing transport encryption to SMTP. A few major MTAs (such as Postfix, Cloudmark and Halon) supports it, and a growing number of domains are being signed.
If domain is DNSSEC-signed, but its DNS server fail to give proper answers in response to TLSA queries, email delivery to this domain will fail for senders using DANE. The most common problem is servers responding with SERVFAIL.
This is a verified list of DNSSEC-signed domains, which doesn't give proper TLSA responses, and therefore needs to be excluded from DANE verification, in order to have email delivered to them.