configure spamassassin to only check incoming email

[Gijs]

Hey list,

I'm using sendmail to handle all my incoming and outgoing email and now 
I've ran into a problem related to spamassassin.
Because spamassassin also checks outgoing mail, sending outgoing mails 
always takes about 3-4 seconds.
Normally this wouldn't be a problem, but my boss wants to send a 
newsletter every month to quite a number of users, and this is undoable 
if it takes 3-4 seconds per email.

I've tested it without spamassassin and it only took like 0.3-0.5 
seconds, which is doable.

Another solution to my problem is ok as well, as long as the send-time 
gets decreased to around <0.5 seconds.

Regards,
Gijs