[exim] problem with interface string expansion

Hi all,


I'm using this construct to select an outgoing interface:

dkim_smtp:

driver = smtp
max_rcpt =9
dkim_domain = $sender_address_domain
dkim_selector = biz
dkim_private_key = /etc/exim/private.key
dkim_canon = relaxed
multi_domain = false
interface = <;${lookup mysql{Q_OUTGOING_INTERFACE}};$received_ip_address


the Q_OUTGOING_INTERFACE query returns either an empty string or an IP
address.

In the case of an empty string exim should choose from the rest of
values, e.g. $received_ip_address

But in all cases I get this error, like expansion never happened:

R=dnslookup T=dkim_smtp defer (-1): "" is not a valid IP address for
the "interface" option for dkim_smtp transport

What can I do to get full debug on a transport ?


Using centos 7 with default exim-4.84.2


Thanks,

Marius