CHECKRECIPIENT - Check Recipients during SMTP

IndiMail has a feature called CHECKRECIPIENT which allows indimail to check at SMTP, if the recipient to whom the mail is being addressed exists. It is always better to reject such users at SMTP rather than later during the actual delivery to the mailbox. Due to spam, in most of the cases, the Return Path will be forged or undeliverable. Hence you will be left with a condition where plenty of bounces will be left on your system, impacting the performance of your messaging system.

CHECKRECIPIENT can be also be used to reject mails for inactive users, overquota users and users who do not have the privilege to receive mails. CHECKRECIPIENT can be enabled by setting the environment variable CHECKRECIPIENT to one of the following values

1. Reject the user if not present in IndiMail's MySQL database
2. Reject the user if not present in IndiMail's MySQL database and recipients.cdb
3. Reject user if not present in recipients.cdb

You can selectively turn on CHECKRECIPIENT for selective domains by including those domains (prefixing the domain with '@' sign) in the control file /etc/indimail/control/chkrcptdomains.

If the environment variable MAX_RCPT_ERRCOUNT is set qmail-smtpd will reject an email if in a SMTP session, the number of such recipients who do not exist, exceed MAX_RCPT_ERRCOUNT.

CHECKRECIPIENT also causes the RCPT TO command to be delayed by 5 seconds for every non-existent recipient, to make harvesting of email addresses difficult.

If you do not have large number of users

% su
# echo 1 > /service/qmail-smtpd.25/variables/CHECKRECIPIENT
# svc -d /service/qmail-smtpd.25
# svc -u /service/qmail-smtpd.25
# exit
%