What IPv6 Means for Email Senders

If you hang out with techies or follow tech-news, you may have heard that the world is running out of IPv4 IP addresses and that it will be replaced by the IPv6 protocol so everyone who wants an IP address can still have one. That’s good news and one less thing to worry about.

Or is it? The transition is set to change email marketing, blacklisting and email deliverability in the future. This is what you need to know:

The abridged technical background of IPv4 and IPv6[1]
IP addresses are assigned to devices on the Internet for identification and location definition to exchange data within or between computers. The first major version of IP is Internet Protocol Version 4 (IPv4) and assigns approximately 4.3 billion IP addresses to users in ranges from to

However, as far back as the late 1980s, it was realised that we would eventually face a depletion of the pool of unallocated IPv4 addresses and need more than the potential 4.3 billion IP addresses if the internet continued to grow and IPv4’s successor, Internet Protocol Version 6 (IPv6) was created and these systems are currently running in parallel. But although the predicted IPv4 address exhaustion was already evident in 2008, only about 4% of ISPs worldwide of Internet services and software vendors have deployed IPv6 and it will appear that the transition will not be seamless in all aspects.

IPv6 address uses 128-bit addresses that are represented as eight groups of four hexadecimal digits separated by colons, for example 2001:0db8:85a3:0042:1000:8a2e:0370:7334 and will create 3.4×1038 addresses – that’s a lot for now and perfect timing too with the anticipation of the “internet of things” on the horizon.

With IPv4, a company or a small Internet Service provider (ISP) would get IP addresses in blocks of around 1000 addresses that they would assign to their customers. For example, they’ll allocate one IP address per server, or bigger customers would get blocks of four or eight IP addresses. With IPv6, it means that in future ISPs will easily get a million IP addresses and give each customer a few dozen for each of their devices, instead of the one or two they assign now.

Blacklisting and reputation
Spam control is one threat that is not entirely addressed in the migration from IPv4 to IPv6.

IP blacklisting is the method most often used to curb spam and adds IP addresses to a blacklist when the IP address is confirmed as a “bad” site. One way spammers avoid blacklisting is by switching to a new IP address as soon as one of theirs is blocked but because the supply of IPv4 IP addresses is low, it is becoming harder for them to do. However, with IPv6 they’ll no longer get one address or just a few that are easy to block and they’ll be able to change IP addresses easily.

So while blacklisting is successful in IPv4, with IPv6, the technique may no longer be possible due to the immense number of addresses to be blacklisted. Additionally, by the time a domain is verified as a bad site and added to a blacklist, its IP address has already changed.

How IPv6 affects email marketers
So, what will happen to email and blacklisting in future? The answer is not quite clear yet. In fact, in draft document from the IETF (The Internet Engineering Task Force) about e-mail migration to IPv6 confirmed that there are still many unknowns when they stated that, “The lack of a full understanding of all abuse threats SHOULD NOT preclude the adoption of IPv6 for mail. A comprehensive understanding of threats will not be available until implementation.”

Despite there being no clear direction, what IPv6 means for email is that there are different schools of thought on how to handle spam once IPv6 is more widely adopted. Some experts in the field are suggesting that while IPv6 will be ineffective to block individual IP addresses, a solution may be to blacklist blocks of IP addresses if spam behaviour is detected. The risk is obviously that it will result in collateral damage for the legitimate senders within the block of IP addresses.

Another solution is to approach the problem from another angle, instead of blocking IP addresses, trusted email servers are identified, and only email from such sources will be delivered. The argument is that the number of email servers is not as vast compared with the number of IP addresses.

Whichever way the blacklisting or spam prevention trends are heading, it is clear that sender reputation will remain your best defence against being branded as a spammer and having your email deliverability rates plummet.

Guard your sender using only verified domains, with a good reputation, in the “from,” “reply to” and return path address, as well as the domains appearing in links in the e-mail body. Avoid, as far as possible, falling prey to spam traps and never, ever use purchased lists. These elements, together with the content, layout and design and other components  of the email will continue to determine the fate of your campaigns and will in future carry more weight than the labelling of the IP address.

In the meantime though, IPv4 is here to stay and it may be a while before companies start moving to IPv6. Continue practicing consistent good list hygiene. After repeated bounces, bad or non-existent emails must be removed or you risk be labelled a spammer, regardless of whether you are using IPv4 or IPv6. You are also assured that by following the basics of good email marketing practices, your recipients will continue to engage with your messages and your complaint rates remain will remain low. In which case, neither IPv4 nor IPv6 will prove a significant hurdle while the experts are figuring out how to handle the spam problem in future.

[1] http://en.wikipedia.org/wiki/IPv6, http://en.wikipedia.org/wiki/IPv4_address_exhaustion, http://en.wikipedia.org/wiki/Internet_Protocol