Whenever your mainl server sends to or receives email from other servers, it broadcasts a greeting that looks somewhat like this:

220-your.hostname ESMTP Exim 4.68 #1 Tue, 06 May 2008 19:33:44 -0700
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.

To edit this greeting, you can edit the following section in /etc/exim.conf:

smtp_banner = "${primary_hostname} ESMTP Exim ${version_number}
#${compile_number} ${tod_full} n
 We do not authorize the use of this system to transport unsolicited, n
 and/or bulk e-mail."