exim - Could not complete sender verify callout
I am new to exim so please excuse if it is a silly question. I am not new to Linux or Network Administration in general.
I need a fast solution because I have a server where users can't receive their e-mails. Any help is really really appreciate. :)
The server (FC4 + cpanel) runs exim 4.52
The configuration is standard, no special things. It wasn't configured by me, but now I am in charge..:)
There are a lot of mails in exim_reject rejected with: Could not complete sender verify callout
There are also authentic domains (ex: mail.citigroup.com ) for which emails are rejected.
2006-03-26 04:11:54 H=(mail.xxx.com) [x.x.156.26] F=<firstname.lastname@example.org> temporarily rejected RCPT <email@example.com>: Could not complete sender verify callout
I've read something about exim verifications and I understood how the whole thing (callout verification) works: the server tries a smtp connection with the sender server and if something goes wrong the message is rejected. This is mainly because of wrong configured servers and MX records. It I am wrong please correct me.
What I want to do, is to configure the server to exclude some domains which are not spam-senders.
How can I accomplish that?
I've read about sender_verify, sender_verify_hosts *, sender_verify_hosts_callback *, sender_verify_callback_domains ! *.some.domain :* but I don't know where in exim.conf to set them. When I restart exim after I add these option I get an error:
Please tell me how can I exclude some domains from this verification, and where in exim.conf to add the new options.
Starting exim-smtps: 2006-03-27 22:50:56 Exim configuration error in line 29 of /etc/exim.conf:
main option "sender_verify_callback_domains" unknown
Thanks for your help