Some mail servers (MX hosts) have associated TLSA records with certificate usage 2 (DANE-TA) that match the just retired Let's Encrypt issuer CA ("X3"). All Let's Encrypt users publishing DANE-TA(2) TLSA records need to update their TLSA records to publish records that match the current intermediate issuer CAs.

In more detail, there are multiple Let's Encrypt issuer certificates that may be used in automated certificate renewals: two primary certificates ("R3" and "E1") and their emergency backups ("R4" and "E2"). Thus, SMTP server operators using DANE-TA(2) with Let's Encrypt certificates must publish the following list of TLSA records (possibly in addition to "3 1 1" records matching the server public key) for each of their MX hosts in order to prevent delivery failures:

CA tagRecommended TLSA Records to match Let's Encrypt issuer CAs IN TLSA 2 1 1 60b87575447dcba2a36b7d11ac09fb24a9db406fee12d2cc90180517616e8a18 IN TLSA 2 1 1 276fe8a8c4ec7611565bf9fce6dcace9be320c1b5bea27596b2204071ed04f10 IN TLSA 2 1 1 bd936e72b212ef6f773102c6b77d38f94297322efc25396bc3279422e0c89270 IN TLSA 2 1 1 8d02536c887482bc34ff54e41d2ba659bf85b341a0a20afadb5813dcfbcf286d IN TLSA 2 1 1 e5545e211347241891c554a03934cde9b749664a59d26d615fe58f77990f2d03

The "X3" hash is no longer needed, all certificates issued via "X3" have now expired, and all replacements are using "R3" or "E1".

MX hosts whose TLSA records include only the "X3" digest will shortly be unable to receive email from sending systems that perform DANE validation.

Please avoid issuer TLSA records with selector Cert(0), i.e. "2 0 1" and "2 0 2". These are much more fragile, and worse, "R3" and "R4" are cross-signed by two different issuers, so there are two differnt full cert hashes for R3 and R4, but just one underlying public key and corresponding "2 1 1" hash.


The MX host table below is sorted to list hosts that serve the most domains at the top.

signed domainshost name