mail and IPv6, not The Reg does 240/4

Thu Feb 15 20:01:21 UTC 2024

On Wed, 14 Feb 2024 18:25:03 -0800
Stephen Satchell <list at satchell.net> wrote:

> On 2/14/24 4:23 PM, Tom Samplonius wrote:
> > The best option is what is happening right now:  you can’t get new IPv4
> > addresses, so you have to either buy them, or use IPv6.  The free market
> >   is solving the problem right now.  Another solution isn’t needed.  
> 
> Really?  How many mail servers are up on IPv6?  How many legacy mail 
> clients can handle IPv6?  How many MTA software packages can handle IPv6 
> today "right out of the box" without specific configuration?

	Mine have been dual stack for a while (6 years?  8 years? don't
exactly recall).  However, I remember being enough of an early v6
adopter that it was a bit of a challenge to get IPv6 glue records set
up for our DNS servers (that was long before I was brave enough to have
my email servers on v6, though).

> Does any IPv6 enabled ISP provide PTR records for mail servers?

	We do, of course, I can't speak for others.  We also
sub-delegate on request.  However, we are small/local and cater to small
businesses.

> How does Google handle mail from an IPv6 server?

	I remember Google being where some of my first v6 email was
coming from and going to.

	I would advise that if you allow your MTA to attach to all IPv6
addresses that you make sure all of them have REV PTR.  Google, at
least last time I looked, would deny email via IPv6 based solely on REV
PTR errors.  They are more forgiving over v4, but I suspect that
has/had to do with more mature spam filtering considerations on v4 than
v6.
	I once made the mistake of not having one of my secondary
addresses set up with a REV PTR and Google rejected any email that came
from that IP.

--TimH