Showing posts with the label dns

Help! I'm seeing 550-5.7.25 errors at Gmail!

Are you seeing this error message when trying to send emails to Gmail? 550-5.7.25 The IP address sending this message does not have a PTR record setup, or the corresponding forward DNS entry does not match the sending IP. As a policy, Gmail does not accept messages from IPs with missing PTR records. For more information, go to https://support.google.com/a?p=sender-guidelines-ip To learn mor…
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Help! Domain of sender address does not resolve!

Are you trying to send email and seeing it rejected with "Domain of sender address does not resolve" or "Unresolvable RFC.5321 or RFC.5322 from domain"? These SMTP rejections are telling you that something is missing from your DNS. Microsoft , Yahoo and oth…

Lookalike domain finder: Fun with homoglyphs and more

Here's a cool tool that a colleague at Valimail created recently, and if you care about protecting against people spoofing your emails through lookalike domains, I think you might find it interesting. It's Valimail's Domain Lookalike Finder , created by VP of produ…

DELIVTERMS: TTL

Today on DELIVTERMS , the series here on Spam Resource where we help decode email and deliverability terminology, we're digging into something that's absolutely everywhere in DNS but rarely explained in plain language: TTL. It stands for "Time To Live." And in…

Seeing AT&T Reverse DNS issues when sending mail?

Example SMTP Errors When sending email messages to the various AT&T consumer email domains (ameritech.net, att.net, bellsouth.net, currently.com, flash.net, nvbell.net, pacbell.net, prodigy.net, sbcglobal.net, snet.net, swbell.net, wans.net, worldnet.att.net) recently, you …

Delivterms: PSL aka Public Suffix List

It’s time to decode another deliverability definition. PSL stands for the Public Suffix List , and it’s one of those things that a certain subset of email geeks (and maybe web developer geeks) find very valuable. What does it do? DMARC.org explains : “It [is a list that] was cr…

DELIVTERMS: DNS aka Domain Name System

Let’s decode another acronym! DNS is a term not limited to email deliverability, but it sure does show up there quite a bit. And it stands for: Domain Name System. DNS is the phone book or address book of the internet. You type “ www.google.com ” into a web browser. The web bro…

Flapping DNS and what to do about it

Has this one ever happened to you? Your DNS record is there – and then it’s not. Or it’s there when you check certain DNS servers, but not others. Or you hit “reload” on a DNS lookup tool (like, perhaps, Wombatmail ) and the results aren’t consistent. Hit reload 5 different ti…

Don't double up on DMARC

Here's a new oops that I've observed a few times recently! In case you didn't know already, you can't have two DMARC records for your domain name. (I'm not talking about subdomains ... I'm talking about specifically having two DMARC DNS records at the sa…

MX records changing for Microsoft-hosted domains ... eventually

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…

Microsoft errors: 5.4.4 (unable to route: no mail hosts for domain)

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, her…

Everything broke last week

So much going on in the past week in the world of email deliverability. Multiple email platforms (ISPs/MBPs) and sending platforms (ESPs) having problems or unexpected downtime. Multiple issues with DNS, which is one of those things that few people understand and even fewer peo…

Wombatmail is still here for all your DNS needs

Did you know? For the past fifteen years, I've run a simple little website called Wombatmail  that provides a set of DNS lookup tools. My goal was to have a simple set of tools to help you troubleshoot DNS issues. You can do things like look up DMARC settings for a domain,…

Yahoo problems? Could be SOA record issues in DNS

Are you seeing this bounce message when trying to send mail to Yahoo subscribers? 451 Message temporarily deferred due to unresolvable RFC.5321 from domain; see https://postmaster.yahooinc.com/error-codes And you've checked and confirmed that your sending domain seems to re…

Spamhaus is not blocking Gmail

A friend warned me of a scenario that could have the potential to freak people out, if misunderstood. It looks like this: This person is using Spamhaus to filter inbound mail. They seem to be rejecting mail from Gmail due to a Spamhaus listing. The Spamhaus website DOES suggest…

Learn how DNS works with this new zine

Julia Evans aka b0rk is somebody smart that I follow on Twitter. She created this super cool tool that I've linked to on social media before, called Mess with DNS , providing you with a safe space to learn about DNS by doing -- letting you set up DNS records under a test …

Spamhaus Blocklist Changes

Speaking of Spamhaus, this just popped up in my RSS feed reader. It looks like Spamhaus is going to take a harder stance against users who query their lists via open or public DNS systems (such as Google Public DNS or Cloudflare's 1.1.1.1 Service). They're going to r…

XNND.com is 11 years old today

I've long had a little banner at the bottom of my xnnd.com DNS tools site that says "since 2008" but it looks like I'm going to have to change that. Looking through my notes, the site actually launched eleven years ago today! XNND exists because back then t…

Cloudflare Launches 1.1.1.1 DNS Service

Cloudflare just launched their own public DNS service . To try it, simply configure your computer to use the DNS servers 1.1.1.1 and 1.0.0.1 . Then your computer's DNS lookups (the internet's mapping of domain names to IP addresses) will route through Cloudflare instea…

How to Optimize Your SPF Record

Steve Atkins of Word to the Wise just released a cool new tool: SPF Minimizer . Over on the Word to the Wise blog, he explains how it works and provides an extremely insightful explanation of do's and don'ts when it comes to SPF, aka Sender Policy Framework.