[SA-exim] distinguishing fetchmail from others

[Ross Boylan]

I'd like help using sa-exim with fetchmail.  Recent network
alterations have forced me to use fetchmail, which I know is not a
natural combination with acceptance-time scanning.  I'm hoping it's
temporary.

My old rules didn't scan any locally originating mail, but everything
coming through fetchmail appears local.  Something's got to change if
I'm to have any spam checking.  I need some way to distinguish
fetchmail from other sources of email.  Further, within the mails
retrieved by fetchmail some will be from me (as I cc myself), and I'd
like to avoid scanning them.

Does anyone have any suggestions about how to accomplish this?

My current thinking is that I need to tell exim4 to listen on a second
port (umh, is there some natural choice?) and have fetchmail deliver
to that port.  I think the port will be available for SAEximRunCond.

BACKGROUND

I'm running sa-exim on a Debian testing (aka etch, basically same as
just released sarge) system. sa-exim 4.2-2; exim4 4.52-2.

FALSE LEADS
Here are some approaches I don't think will work.

fetchmail provides no easy way to add a header that would tag the
email (I seem to recall it used to have this feature, but don't see it
now, in 6.2.5).

I think sa-exim runs before exim routers, so having routers add
headers also won't work.

I think that the application of SAEximRunCond can not itself be made
conditional on anything (e.g., port of incoming message).  That is,
the condition can test the port and expand to false, but I can't
control whether or not the condition is run or the sa-exim scanner is
used at all.

I'm assuming sa-exim operates using exim's local scann function hook.
Right?

Thanks for any help.
Ross Boylan