I beleieve that every information system has the needs to send emails.
Currently PostgreSQL doesn't have a function which gets TEXT and return true if it's valid email address (xxx@YYY.com / .co.ZZ)
Do you believe such function should exist in PostgreSQL or it's best to let every user to implement his own function?
I don't think so this functionality should be in upstream - but it is good use for some extension and placing it in PGXN or PostgreSQL community repository.
Postgres has good regexp support and this case can be implemented by one regexp.
you can use PLPerlu and use some modules from CPAN