I agree on the levels of abstraction.

How will SPF work in with this?

On Fri, 30 Mar 2007 18:53:38 +1000, Sean N. Heukels sean@reeve.nl wrote:

Wanted to make you aware of the following

http://trac.roundcube.net/trac.cgi/ticket/1484202

(transcript)

Ticks in messages are allowed -

Is it an option to add an option that does advanced mail address
checking? sample functions exist that level 1 check MX record, level 2 check for
existance of the remote mail name. Level 0 can be no check - current functionality.

Addin this would be very simple, also we can set the option defaulting
to level 0

link: http://www.devshed.com/c/a/PHP/Email-Address-Verification-with-PHP/

I think we can make some easy improvements here ....