Best practice TLSA RRs for CA-issued certs

Michael Grimm trashcan at
Thu Dec 29 21:53:05 CET 2016

On 29 Dec 2016, at 20:56, Patrick Domack <patrickdk at> wrote
> Quoting Michael Grimm <trashcan at>:

>> #) Would it be possible to get *two* distinct LE certificates, one for the IMAP and one for the webserver ..
>> #) .. and simultaneously *keep* my selfsigned certificate for the the mailserver ..
>> #) .. and forget about the issues mentioned above?
>> #) Or should I strictly separate my mailserver from the rest by means of distinct domains, instead?
> You can get multiple certificates, I have several myself in a single domain, and so this same thing.

Thanks for your feedback. Then I will gor for that.

> I am using an LE certificate for my DANE TLSA records, and I do have the auto-rotation script update the TLSA entry. While this is as simple as it sounds, dnssec makes it more complicated.

> You have to remember your dns ttl and and dnssec rrsig ttl and rrsig expiration for the given entry. I have switched to using dns slave servers and in my implementation that means dnssec rrsig values are signed valid for a week, so I don't push out the new certificate from LE, till two weeks after I added the TLSA dns record, to be safe.

See my answers to Viktor. I am very hesitant when it comes to human intervention. Thus, I will avoid it.

> The only issue I have had with selfsigned certs is that some mailservers will not send you email if you use one, since the sender has turned on certificate verification, and it will not fail back to non-encrypted to send email. This is mainly a misconfig on their part, but it matters if you want email from them. This has been very minimal impact, but I have seen it a few times.

I haven't run into that issue, yet, luckily. If that will happen to my users, I will have to take the burden and apply LE certificates for port 25 as well. But until that time, I will avoid human intervention into a process where two autorotation tools go for "incompatible" tasks :-) Or is there one single tool dealing with DNSSEC, TLSA rotation, and LE upgrades on the market?

Thank you for your valuable input and with kind regards,

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