A new erratum update is available for Univention Corporate Server 4.0.
It is applicable to the following patch-levels: 2.
It addresses the following problem:

Program component:  univention-mail-postfix
Reference:          bug 37653, bug 38292
Fixed version:      9.0.3-4.260.201507231625

This update addresses the following issues:
* Add options to check IP-FQDN-mapping as a means to fight spam. Adds two
  new UCR variables:
  mail/postfix/smtpd/restrictions/sender/reject_unknown_client_hostname and
mail/postfix/smtpd/restrictions/sender/reject_unknown_reverse_client_hostname
  for weaker and stricter reverse DNS checking respectively.
* To configure the max. number of concurrent Amavis processes, a new UCR
  variable is introduced: mail/antivir/max_servers. When unset, the
  current default "2" is used.

We recommend to update your UCS installation. Updated packages are
available in the Univention online repository, which is automatically
added to the apt packages sources. The following procedures can be
used to update a UCS installation:

1. A single system can be updated in the web interface of the
Univention Management Console through the "Software update" module.

2. A single system can be updated on the command line by running the
command "univention-upgrade"

3. Multiple systems can be updated through a maintenance policy.

Additional information can be found in the UCS manual.