Merge pull request #5 from AlwindB/patch-1

Update DANE-for-SMTP-how-to.md
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@ -412,6 +412,93 @@ Successful delivery to <danedomain@example.nl> (retry 0) in 2.108s: 2.0.0 exampl
Deleting mail file (all recipients done)
```
# Implementing DANE for SMTP on Port25 PowerMTA (outbound e-mail traffic)
Various Email Service Providers (ESP) are using Port25 PowerMTA as their preferred outbound MTA.
Port25 has build-in support for DANE since version v5.0
**Specifics for this setup**
* Port25 PowerMTA v5.x+
**Assumptions**
* Basic configuration of PowerMTA
* TLS Certificate already in place
* STARTTLS active (`use-starttls yes`)
* DNSSEC capable DNS resolver
## Generic configuration
### Configure the use of DANE on the domain level
Within the configuration of a specific domain
```
<domain example.com>
use-dane true
</domain>
```
Within the configuration of all domains
```
<domain *>
use-dane true
</domain>
```
If TLS is required per DANE for SMTP `use-starttls` and `require-starttls` will be overridden.
### Logging
By enabling the resolver logging (`log-resolution yes`) you are able to see the DNS queries for the TLSA records.
Within the configuration of a specific domain
```
<domain example.com>
log-resolution yes
</domain>
```
Within the configuration of all domains
```
<domain *>
log-resolution yes
</domain>
```
By enabling the TLS logging (`log-tls yes`) you are able to see the TLS DANE verification.
Within the configuration of a specific domain
```
<domain example.com>
log-tls yes
</domain>
```
Within the configuration of all domains
```
<domain *>
log-tls yes
</domain>
```
Example logging:
DNS Resolver
```
Starting new query for TLSA _25._tcp.jail.internet.nl:
answer _25._tcp.jail.internet.nl. 3600 IN CNAME 3.1.1._dane.internet.nl.
answer _25._tcp.jail.internet.nl. 3600 IN CNAME 3.1.1._dane.internet.nl.
answer 3.1.1._dane.internet.nl. 3600 IN TLSA 3 1 1 25DE2127E359B8522DDD6E237381458804549CDE5440E4F5B547C5629E48D46B
_25._tcp.jail.internet.nl. 3600 IN CNAME 3.1.1._dane.internet.nl.
_25._tcp.jail.internet.nl. 3600 IN CNAME 3.1.1._dane.internet.nl.
3.1.1._dane.internet.nl. 3600 IN TLSA 3 1 1 25DE2127E359B8522DDD6E237381458804549CDE5440E4F5B547C5629E48D46B
```
TLS Logging
```
tls: TLSv1.2 connected with 256-bit ECDHE-RSA-AES256-GCM-SHA384
tls: cert: /C=NL/ST=Zuid-Holland/L=Den Haag/XXXXXXX; issuer=/C=NL/O=XXXXXXX; verified=yes
tls: DANE match: /C=NL/ST=Zuid-Holland/L=XXXXXX; issuer=XXXXX; depth=0
```
# Special thanks
Our infinite gratitude goes out to the following people for their support in building this how-to for DANE.