sendmail adds $j to header addresses

By default, sendmail will append the canonical domain name ($j) to any header address without a domain (e.g. From:, To:). This can be confusing to users, as it can make UCE appear to originate from your sendmail system.

For example, assume the FQDN of your sendmail system is The envelope sender address is, and the header sender address is From: Spammer (with no domain name).

sendmail will append to the header sender address, and the recipient's Mail User Agent (MUA) will display the following:


To instead append the envelope sender domain to header addresses without a domain, add the C flag to the appropriate mailer (likely ESMTP). The header sender address will then appear as:


.mc file change:

Note: You may want to make .mc file changes for other mailers, such as smtp, smtp8, dsmtp, and relay.

Back to
Last modified: 2006/08/01