The problem occurs when there is an entry in local_host_blacklist that is a domain for which the lookup returns a SERVFAIL.
I rigged a DNS record so you can test this: add fail.30hopsmax.at to local_host_blacklist. As long as that entry is there, every icoming email (not only for this one domain) is rejected with a 451 temporary error. One problem is that the documentation explicitly states that hostnames are fine: exim4_files(5) /etc/exim4/local_host_blacklist is an optional file containing a list of IP addresses, networks and host names [...] conf.d/acl/30_exim4-config_check_rcpt (and exim4.conf.template) # deny bad sites (IP address) # CONFDIR/local_host_blacklist holds a list of host names [...] Should this be considered a documentation bug? hop -- What should you do to a blue elephant? Cheer it up.
smime.p7s
Description: S/MIME cryptographic signature