exim - Could not complete sender verify callout
 

Hi,
I am not very experienced with exim. In fact I used only sendmail and now I face a sever where exim is in action :):)

On one of my servers I get a lot of rejected mails which aren't spams or other malware.

ex:
I am using cpanel, but I would prefer to edit the configuration manually.

How can I disable the verifying process only for some domains?

I’ve read about:sender_verify, sender_verify_hosts , sender_verify_hosts_callback, sender_verify_callback_domains but I don’t know how to effectively use them.

The whole process exim uses for verifying senders is a little confusing for me at this point. I would really appreciate if someone could explain to me how this works or point me to some good resources.

Thanks

sender_verify runs the from address through the directors and routers and checks if they could deliver to that address. For local addresses this means the local part is checked for remote addresses this only checks whether the domain is ok in the sense that there's a (mail)route to it. Host exceptions are entered through the sender_verify_hosts.

eg
sender_verify
sender_verify_hosts ! *.some.domain

verifies that the routers and directors know how to handle the sending address except for *@*.some.domain

sender_verify_hosts_callback does a lot more: it initializes an smtp connection to the remote site and sends HELO, MAIL FROM:<>, RCPT TO <the address to be verified>, QUIT. This is disabled by default since it's taking a lot of resources. To enable the host handling the from address must match all of

sender_verify_hosts
sender_verfiy_callback_domains
sender_verify_hosts_callback

So, to exclude a certain domain from callback verification you could do

sender_verify
sender_verify_hosts *
sender_verify_hosts_callback *
sender_verify_callback_domains ! *.some.domain :*

(The :* can be omitted as it is implied when host list end with a negative item)

Unless you have a really small amount of mail to handle you should probably switch the callback off by default.

Thanks, a lot for your clear explanation :)