Ask HN: Tools for collating and creating digests from multiple emails

For some time our team has been looking for a tool to take all the emails from our servers & external services and perform collation / pattern grokking / send out digests & perform general magic.

* We must be able to run this tool ourselves (i.e. not a cloud service)

* We'd like to receive digested / grokked emails from cron jobs / builds / package updates etc... rather than getting individual emails.

* We'd like to look for keywords like 'critical, security, failure' and raise their priority to send them out sooner.

* A web interface would be really nice, but not required.

* Preferably Open Source.

Any ideas?