[Exim] filtering at SMTP DATA time?

Can standard Exim do any filtering (like regular expressions) as SMTP DATA
time?

So a message can be rejected at end of DATA?

I read in Exim 4.30 Specification chapter 14 that exim filters is applied
at the start of each delivery attempt. So I assume that could be long
after the SMTP QUIT.

Could this be done with acl_smtp_data policy control using "condition" and
"match"? If so, any examples available?

I read that add-on exiscan-acl adds a "regex facility". Is that the
recommended (or only) way to do this before server sends acknowledgement
of DATA?

I am hoping to learn how to do this without any add-on.

If this question has been asked before, please add to the Exim FAQ.

Please carbon-copy me on all replies.

Thank you,

  Jeremy C. Reed
...................................................
     BSD software, documentation, resources, news...
     http://bsd.reedmedia.net/