mx records

If you’re one of those weirdos (like me) who tracks what email providers hosts mail for what domains, you’ll want to take note of this. In the email industry’s ongoing efforts to improve email security, Microsoft is adding the ability for Microsoft-hosted domains to implement DANE with DNSSEC. As Microsoft explains, “SMTP DANE is a security protocol that uses DNS to verify the authenticity of the certificates used for securing email communication with TLS and protecting against TLS downgrade attacks. DNSSEC is a set of extensions to DNS that provides cryptographic verification of DNS records, preventing DNS spoofing and adversary-in-the-middle attacks to DNS.” Anyway, my point is not to dissect the potential value of DANE or theorize how long it’ll take for a majority of customer domains to be updated (Microsoft hosts mail for 750,000 of the top ten million domains, and I’m sure many more beyond that). Instead, I

When sending to Microsoft OLC (Outlook Consumer – i.e. hotmail.com, outlook.com, msn.com, live.com, etc.) domains, are you seeing this bounce message?Microsoft: 5.4.4 (unable to route: no mail hosts for domain)If you’re seeing that error message, or something similar, here’s what’s happening, I think, based on what some smart folks have shared with me.All of those domains have an MX record that points to outlook-com.olc.protection.outlook.com. And when you look up the IP addresses for that server mentioned in the MX record, what do you get? Well, when I do it from here, I get just two IPs: 104.47.58.33 and 104.47.55.33.But other folks showed me examples where they were receiving 25+ IP addresses in response. I can’t reproduce it, so I don’t know if it’s geo-specific, intermittent, or if overall, the whole thing has been addressed. I suspect some combination of all of that. But anyway, I’m told that when the results

Let’s compare B2C versus B2B deliverability issues, shall we?In the B2C (business-to-consumer) or DTC (direct-to-consumer) email marketing universe, the number of mailbox providers, while broad, is very heavily concentrated in the US. There are six providers, that when you add up their subscriber reach, they comprise over 90% of almost any typical US B2C email list: Google, Yahoo, Microsoft, Comcast and Apple. Anything beyond the top five is pretty much in the long tail. (That doesn’t mean you ignore deliverability issues for smaller providers, but when you do a cost/benefit analysis of time investment versus reward, it is often clear that fixing an issue with a big provider first will yield more benefit.)In the US B2B (business to business) email universe, things are not as obviously concentrated. There are more providers and it’s not just a set of six controlling just about all of the mailboxes you’ll want to send mail