John Hesch

Whitelist For Exim Sender Verify Callout

Recently a user called and said that he was not receiving emails from a particular person. The email was being sent, but not received by the user. After verifying that the email was not getting caught up in a spam filter, I looked through the Exim logs located at /var/log/exim_mainlog. I found the email was being rejected with the error

could not complete sender verify callout

Exim by default, will check the senders email address and send a callback to the sending server to check and see if the users email address actually exists. In this case the senders email server was not verifying the email address actually exists and so the email was being rejected.

I didn't want to turn off callouts to verify the existence of email senders so I did some digging and found that Exim allows the callout feature to check with a whitelist to see if a callout instruction should be ignored. The instructions were locked within the cPanel forums which require registration and so my Google check didn't find these instructions.

I'm posting them here in hopes that others can find them easily. The original forum post is located here.

Create a file that will be the actual whitelist. In this example it is /etc/whitelist_senders - the addresses need to be listed one entry per line, either the email address or use the wildcard to do an entire domain. To create the file:

In WHM, in the top most edit box add (if there is anything else in the text box add this bellow it):

Still in WHM. scroll down to where there are three text boxes together. This is the begin ACL section. In the middle box scroll down until you find:

and change it to:

Still in the middle box scroll down to the end and change:

to this:

Save and exit. Now try to send and receive email to make sure everything is still working. If all is ok add the address in question to the whitelist and see if it works.

Then put the sender addresses in the file /etc/whitelist_senders, one per line, e.g.

I have been receiving some strange emails lately. The latest one goes like so

Do not reply to this message

Dear Customer,

Our robot has fixed an abnormal activity from your IP address on sending e-mails.
Probably it is connected with the last epidemic of a worm which does not have patches at the moment.
We recommend you to install a firewall module and it will stop e-mail sending. Otherwise your account will be blocked until you do not eliminate
malfunction.

Customer support center robot

A zipped file is attached. I didn't unzip the file but this has all the characteristics of an email virus. As always, never open a file attachment from someone you don't know.

Condiment Conundrum

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