sendEmail trying to use ipv6

[David Fletcher]

That as far as I can tell is the problem but I've no idea what's
causing it. Can anybody help please?

I have a program that I wrote some years ago which runs every night as
a cron job on my Ubuntu server 14.04 (32 bit hardware), to email me
with reminders of things to do. It has a system call to use the
sendEmail utility to do this.

Everything was working just fine until a week or two ago. Now, if I for
example issue the command:-
sendEmail -f dave at thefletchers.net -t davereminder at thefletchers.net -u
Software testing... -m "Reminder by email"

it responds with:-
Mar 19 10:53:41 serveriii sendEmail[25721]: ERROR => localhost:25
returned a zero byte response to our query.

The mail.log entries from postfix are:-
Mar 19 10:53:40 ServerIII postfix/smtpd[25722]: fatal: cannot handle
socket type AF_INET6 with "inet_protocols = ipv4"
Mar 19 10:53:41 ServerIII postfix/master[9323]: warning:
process /usr/lib/postfix/smtpd pid 25722 exit status 1
Mar 19 10:53:41 ServerIII postfix/master[9323]:
warning: /usr/lib/postfix/smtpd: bad command startup -- throttling


My ISP is Virgin Media who apparently is working on implementing IPv6,
but dragging their feet so I don't yet have it available. Because it
looks to me like something is causing sendemail to try to use IPv6, is
there any way to force it to revert to using IPv4, please?

I know a little about networking but I am nowhere near being an expert.

Thanks for any ideas.

Dave