Sender Address Verification

Sender must have legitimate DNS to pass muster
acl_check_rcpt:
...
  require verify        = sender


2004-03-10 00:54:14 H=alias-2.c10-ave-mta1.cnet.com [206.16.1.131] sender verify fail for <CNET_Networks_#3.117100.3336363135383132.b@newsletters.online.com>: all relevant MX records point to non-existent hosts
2004-03-10 00:54:14 H=alias-2.c10-ave-mta1.cnet.com [206.16.1.131] F=<CNET_Networks_#3.117100.3336363135383132.b@newsletters.online.com> rejected RCPT <mark@foster.cc>: Sender verify failed

2004-03-16 01:07:50 H=cm61-18-2-134.hkcable.com.hk (mediadome.net.au) [61.18.2.134] sender verify defer for <jeromefunk_zs@orca.bc.ca>: host lookup did not complete
2004-03-16 01:07:50 H=cm61-18-2-134.hkcable.com.hk (mediadome.net.au) [61.18.2.134] F=<jeromefunk_zs@orca.bc.ca> temporarily rejected RCPT <mdf@ldopa.org>: Could not complete sender verify