We have previously closed several rounds of Horde upgrade because there were "no changes upstream". However it looks like horde stopped upgrading/maintaining "horde framework" and the same modules that we use can be taken from "horde core". It uses different versioning, the latest version is 2.30.2 (for comparision, we use version 5.2.7 or "horde framework"). Latest version of horde core includes changes that we need for PHP 7.2 compatibility. And the latest version of horde framework does not.

Horde library uses deprecated create_function and IDNA varaibles.

For example, this is a fix for create_function
https://github.com/horde/Support/commit/110ffd5983d296c4884289e3f2ad3c698ff922f8

regarding idn_to_ascii and idn_to_utf8, the code is very different upstream
horde: https://github.com/horde/Mail/blob/master/lib/Horde/Mail/Rfc822/Address.php#L139 and https://github.com/horde/Idna/blob/master/lib/Horde/Idna.php#L42
moodle: https://github.com/moodle/moodle/blob/master/lib/horde/framework/Horde/Mail/Rfc822/Address.php#L130