Check_MK now has a new alternative API for notification scripts, which allows them to be configured via WATO. The classical API provided the possibility of a list of strings that was passed to the script in form of variables like PARAMETER_1, PARAMETER_2, etc. The new API passes parameters according to keys of a WATO-configured dictionary, like PARAMETER_FROM and PARAMETER_REPLY_TO.
Two notification scripts have already been converted to use the new API: mail (sending HTML emails) and mkeventd (forwarding to the Event Console).
The configuration of a notification script does only work with the new Rule Based Notifications can be done at two places:
Both configurations are being merged on a per-key basis. That way you can e.g. setup a From: header for your outgoing emails via a global rule, but select various different Reply-To: addresses in different notification rules. If a configuration key appears both in Host & Service Parameters and in a notification rule then the latter one has precedence.
Within that effort the HTML email script has been made far more configurable. You can now configure: