1511: Setup, compose: add note about reverse DNS r=mergify[bot] a=liquidat
## What type of PR?
documentation
## What does this PR do?
If the [mailu setup utility](https://setup.mailu.io/master/) is used with the Compose flavor, in step 4 a list of public host names needs to be provided:
The [first entry in this list is configured as hostname by postfix](ddac2672fc/core/postfix/conf/main.cf (L10)). That is crucial: if the reverse DNS entry for that host is not the same as this first entry in this list, it will be a mismatch between rDNS and HELO, which will lead to bad scoring in many spam filters.
This commit clarifies that point.
It also fixes a missing parenthesis.
### Related issue(s)
- (none)
## Prerequistes
- (none applicable)
Co-authored-by: liquidat <liquidat@bayz.de>
88ffb9fcf1
