Blocking spoofed mails going out from your cPanel/WHM server to protect it from blacklists

1. Login to WHM >> EXIM CONFIGURATION MANAGER >> ADVANCED EDITOR

2. Add the following entry using the Add additional configuration setting feature:

1. domainlist remote_domains = lsearch;/etc/remotedomains

3. Under the section “ACLs“, add the following code in acl_not_smtp >> custom_begin_outgoing_notsmtp_checkall :

1. deny
2. condition = ${if ! match_domain{${domain:${address:$h_From:}}}{+local_domains : +remote_domains}}
3. message = Sorry, you don't have permission to send email from this server with a header that \
4. states the email is from ${lc:${domain:${address:$h_from:}}}.

4. Search for acl_smtp_data and add the following lines undercustom_begin_outgoing_smtp_checkall :

1. deny
2. authenticated = *
3. condition = ${if or { \
4. { !eqi{$authenticated_id} {${address:$header_From:}} } \
5. } }
6. message = Your FROM address ( $header_From ) must \
7. match your authenticated email user ( $authenticated_id ). \
8. Treating this as a spoofed email.

Important points to keep in mind:

1. POP before SMTP won’t work. You will have to ask your customers to use the option – “My Server Requires Authentication” in the SMTP settings of their email client.
2. Username in the format user+domain.com will not work. Customers will have to use [email protected] instead.