Need some advice on appropriate PL strategy...

I'm in the process of implementing a "monitor this" type feature on a
web-application. When something changes on the monitored item an email
to the subscriber is generated. I'd like to do this via triggers
instead of application logic. As far as I can tell pl/pgsql does not
include any method for e-mailing as a function side-effect. So I need
to choose a different PL. The function is basically a series of
queries, coupled with a mailing ( look up details of new event; lookup
subscribers and exclude poster of new event from subscriber list, if
present; email subscribers) -- so, aside from the emailing bit, its
trivial in pl/pgsql.

The web application is in PHP, so using pl/PHP could be nice, but I
haven't found a lot of information on pl/PHP to know its relative
maturity/stableness. I'm also familiar with Java, Python, C, much less
familiar with Perl. In order to e-mail will I need a trusted or
untrusted version of the procedural language?

I guess I could alternatively just code up a simple mail function in
another PL and then call that function from pl/pgsql. Is there any
merit to this approach over the "whole-trigger" in another PL method?

Thank you,
Eric Nielsen