That message is caused by a bug in Debian's Postfix package, but the bug didn't just appear last month; it's been there at least since 2012. Probably something that changed on your system last month caused fetchmail to start using the IPv6 loopback address instead of the IPv4 loopback address.
You can fix the bug with the patch provided by Tanguy Ortolo in bug report #723915, or you may be able just to ignore it. It's been happening on my mail server ever since I built it, and hasn't caused any actual harm, AFAIK. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
