pantz.org banner
Gmail and their IPV6 spam filter
Posted on 08-14-2016 22:30:28 UTC | Updated on 08-14-2016 22:33:51 UTC
Section: /software/smtp/ | Permanent Link

Failing forwards

Earlier this week Gmail's servers decided that any email sent from Gmail and then forwarded from pantz.org back to Gmail was now, as their servers put it "likely unsolicited mail". People sending mail from Gmail to pantz.org were getting bounce messages, which looks bad. All other email from any other domain was coming in without issue. I have been forwarding email from Gmail accounts for many years now without issue.

Time to recheck settings

  1. DNS A,AAAA and PTR records for IPV4,6 setup and work correctly
  2. SPF record setup correctly, but this is a forward so it always shows fail. The bounce message passes SPF, so that's nice.
  3. SMTP w/TLS working and available
  4. pantz.org does not modify, remove or shuffle message headers or modify the body of the message in any way.
  5. No increase in spam getting through. pantz.org filters most mail before it is forwarded.
  6. Not using Sender Rewriting Scheme (SRS).
  7. No DKIM setup

The fix

After seeing that everything checked out, I hit up Google to see if anyone else was having this issue. From the results it seems that many people have had this same issue. Some people just started using SRS to fix their issue. Others had to fix their PTR records in DNS. The last group of people had to stop using IPV6 for mail delivery. Since all of the other pantz.org mail server settings were correct, the only thing I could try was implementing SRS or turn off IPV6. Turning off IPV6 delivery was the easiest test. After turning off IPV6 mail delivery, and just leaving IPV4, all mail from Gmail being forwarded through pantz.org was now being accepted again. How dumb is that?

What is up with IPV6?

It seems Gmail has changed a setting (or I hit some new threshold) on their side dealing with only IPV6. Since Google will not tell you why certain mail is considered "unsolicited mail" we can not figure out what was done to try to fix the issue. If I had to speculate on what is happening, my guess is they turned up the sensitivity on email coming from IPV6 as it is obvious that IPV4 filter is not as sensitive. It is not just my server as it is happening to many other people as well.

I had also noticed that mail coming in from a friend whose server delivers mail to my server via IPV6, and then was forwarded to Gmail via IPV6 was being marked as spam every time. According to Google if the user is in your contacts list (and his email address is) the email is not supposed to be marked as spam. That is straight broken. Now that I switched back to just IPV4 delivery, all of his mail is not being marked as spam anymore. I believe Google has an issue with IPV6 mail delivery and spam classification.

What now?

I hate that I had to turn off IPV6 for mail forwarding to Gmail. My next likely step is to implement SRS for forwarding, and see if I can turn IPV6 back on. The best article I found on setting this up on Postfix is here. It also shows how to setup DKIM which might be fun to do as well.

Del.icio.us! | Digg Me! | Reddit!

Related stories


RSS Feed RSS feed logo
About


3com
3ware
alsa
alsactl
alsamixer
amd
android
apache
areca
arm
ati
auditd
awk
badblocks
bash
bind
bios
bonnie
cable
carp
cat5
cdrom
cellphone
centos
chart
chrome
cifs
cisco
cloudera
comcast
commands
comodo
compiz-fusion
corsair
cpufreq
cpufrequtils
cpuspeed
cron
crontab
crossover
cu
cups
cvs
database
dbus
dd
dd_rescue
ddclient
debian
decimal
dhclient
dhcp
diagnostic
diskexplorer
disks
dkim
dns
dos
dovecot
drac
dsniff
dvdauthor
e-mail
echo
editor
emerald
ethernet
expect
ext3
ext4
fat32
fedora
fetchmail
fiber
filesystems
firefox
firewall
flac
flexlm
floppy
flowtools
fonts
format
freebsd
ftp
gdm
gmail
gnome
greasemonkey
greylisting
growisofs
grub
hacking
hadoop
harddrive
hba
hex
hfsc
html
html5
http
https
idl
ie
ilo
intel
ios
iperf
ipmi
iptables
ipv6
irix
javascript
kde
kernel
kickstart
kmail
kprinter
krecord
kubuntu
kvm
lame
ldap
linux
logfile
lp
lpq
lpr
maradns
matlab
memory
mencoder
mhdd
mkinitrd
mkisofs
moinmoin
motherboard
mouse
movemail
mplayer
multitail
mutt
myodbc
mysql
mythtv
nagios
nameserver
netflix
netflow
nginx
nic
ntfs
ntp
nvidia
odbc
openbsd
openntpd
openoffice
openssh
openssl
opteron
parted
partimage
patch
perl
pf
pfflowd
pfsync
photorec
php
pop3
pop3s
ports
postfix
power
procmail
proftpd
proxy
pulseaudio
putty
pxe
python
qemu
r-studio
raid
recovery
redhat
router
rpc
rsync
ruby
saltstack
samba
schedule
screen
scsi
seagate
seatools
sed
sendmail
sgi
shell
siw
smtp
snort
solaris
soundcard
sox
spam
spamd
spf
sql
sqlite
squid
srs
ssh
ssh.com
ssl
su
subnet
subversion
sudo
sun
supermicro
switches
symbols
syslinux
syslog
systemrescuecd
t1
tcpip
tcpwrappers
telnet
terminal
testdisk
tftp
thttpd
thunderbird
timezone
ting
tls
tools
tr
trac
tuning
tunnel
ubuntu
vi
wget
wiki
windows
windowsxp
wireless
wpa_supplicant
x
xauth
xfree86
xfs
xinearama
xmms
youtube
zdump
zeromq
zic
zlib