Added Global Setting to Server config tab to
  - Enable & Disable the feature
  - Set the Proxy HTTP & HTTPS Ports

Added Per site level switch to enable and disable feature (Located in the Web Tab under the advanced section)

Added Apache2 and Nginx vhost updates to enable proxy_protocol on the listen lines

Added New database column to web_domain called "proxy_protocol" to enable site level config (Patch file Added upd_0089.sql)

Updated the Base Table SQL file to include "proxy_protocol" field

The spamassassin default also has a space, like in install/tpl/amavisd_user_config.master

update databse - strict_mode compatible (https://www.howtoforge.com/community/threads/email-warning-after-modification-of-spam-level.76247/)

Added fields user_config and user_type to the ftp_user table.

First part of fix for issue #3896 - Unknown column 'default_mailserver' in 'field list' when saving client limits main template

This Checkbox can be enabled or disabled by template.

Further I fixed an inconsistent design (HTML) which was introduced by @tbrehm yesterday I tink. (DKIM-Checkbox)