Though disabling IPv6 persistently on reboot was not straightforward and had to be done modifying netplan config, see above on the thread (https://forum.cloudron.io/post/102554).

But if another vps is better I’d happily switch.

What VPS are you on?

Emails are not sending to gmail emails and I need this resolved.

@privsec why would you turn off IPv6 completly ? You can do it but why ? I understood that emails servers from Google and Microsoft are now using full IPv6 resolution and if they receive an email coming from an IPv4 mail server they may or will consider it as spam more easily...

But regarding your question @privsec , how to disable IPv6 completly, I think I would do it on the OS level because I've seen that IPv6 is not enabled inside the docker containers.

First I would start to disable it temporarily using this command as I did in my tests before :
sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1

It will disable ipv6 until next reboot.

And if it works like that for you, then you can reboot your server and try to disable it permanently by creating a new file : sudo nano /etc/sysctl.d/10-disable-ipv6.conf

And you write this in this file :

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1

to save your file and quit nano
CTRL+0 - ENTER - CTRL+X

And then apply this new config file by doing :
sudo sysctl --system

And IPv6 should be disabled completly at the OS level. Reboot your server.

At this point, I just want to future proof myself from IPV6. How do I permanently disable and remove this functionality on my VPS from Netcup.

I do keep getting bounced emails from Gmail.

In that case I would just disable IPv6 altogether from your server network interface. That's the only only thing that worked for me.

I've just found that IPv6 might be enabled at the NetPlan level

Yep this has been discussed above in this thread...from post #52 onward. The solution provided by @joseph worked on my end. I had originally tried something along the line you mentioned (adding link-local: [ ipv4 ] to the yaml file but that didn't work...although I might have done it wrong).

To disable - add to the appropriate yaml file in /etc/netplan - link-local: [ ipv4 ] - on the same level as dhcp instruction. Run netplan try and netplan apply if you are lucky.

That seems to disable IPv6 on Linux.

<rant> Linux start looking more and more like Windows </rant>

I do keep getting bounced emails from Gmail.

What exactly isn't working?

I imagine they are getting bounce to Gmail.

@jdaviescoates said in Email sending broken after updating to 8.2.x (due to IPv6 issues):

Have you set up the ipv6 reverse dns/ PTR /rDNS record too?

Looks like they have looking at screenshot 2....but possibly badly. I think it should say my.businessdoctorut.com

Though for me, after setting it all up properly I kept getting issues and random bounces with the same error message. Only completely disabling IPv6 from the network interface works (and even that turned out to be a struggle )

its not working again

What exactly isn't working?

Have you set up the ipv6 reverse dns/ PTR /rDNS record too?

These are my screens

From my understadning, it is set up correctly.

yup, this is the culprit. The IPv6 address is statically assigned here. You have to put a # in front of the line to comment it out and reboot the machine.

THANK YOU! That worked.

Seems like netplan is here by default since Ubuntu 18: https://pscl4rke.wordpress.com/2019/10/01/disabling-ipv6-on-ubuntu-18-04-the-netplan-version/

  - "2a03:4000:xx:xx:xxxx:xxxx:xxxx:6007/64"

yup, this is the culprit. The IPv6 address is statically assigned here. You have to put a # in front of the line to comment it out and reboot the machine.

Do you use netplan? If so, I could chek /etc/netplan/50-cloud-init.yaml . Does it have some statically assigned ipv6 block?

I was not aware I did use netplan (I don;t even really know what it is), but yes there is this config file and it seems to contain static IPs, see:

network:
  version: 2
  ethernets:
    eth0:
      match:
        macaddress: "xx:xx:xx:xx:xx:xx"
      addresses:
      - "152.xx.xx.43/22"
      - "2a03:4000:xx:xx:xxxx:xxxx:xxxx:6007/64"
      nameservers:
        addresses:
        - 46.38.225.230
        - 46.38.252.230
        - 2a03:4000:0:1::e1e6
      routes:
      - to: "default"
        via: "152.xx.xx.1"
      - on-link: true
        to: "default"
        via: "fe80::1"

If you tell me how i should modify the file then I'll try it out.

Thanks a lot for your help.

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1

on reboot, cat /proc/sys/net/ipv6/conf/all/disable_ipv6 return 1 so one would think it's all good, but it isn't. curl https://ipv6.api.cloudron.io/api/v1/helper/public_ip still retunrs the IPv6 address and I can still see it in ifconfig for the network interface. Yet manually running either sysctl -p or sysctl -w net.ipv6.conf.eth0.disable_ipv6=1 post boot works just fine to disable IPv6. So there is something at boot time that prevents disabling IPv6.

I therefore went the bulletproof way and disabled ipv6 as a boot argument in grub (GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1"). But then I got of errors at boot time when services start, especially for nginx so that;s not working either.

Any idea?