If you get the following message :
Socket bind() to port 25 for address 127.0.0.1 failed: Address already in use: daemon abandoned
With Exim4, that means that another package is using it.
You have to suht it down.
netstat -lnp | grep :25
You will get something like this :
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 24736/postfix
If this is the case, you have to stop Postfix :
kill -9 24736
It can also be a different module, like Sendmail or Dovecot.