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A hostname lookup failure means that the server to which your email is being sent can't be found. This could be a temporary or permanent error.

I sent an email to someone who I normally email. But now I get a Mail Delivery (Undeliverable) Message back three hours after I sent the original email that says permanent fatal errors and then: Deferred Name Server: xxx.com host name lookup failure Message could not be delivered for three hours, message will be deleted from queue. And then, it says Action Failed Status: 4.4.7 and says Remote MTA DNS etc. I have tried this twice and gotten the same message back. What does this mean? Is it possible that they forgot to renew their domain name? Or could it be that I am now in their spam or something? Thanks for your help!

Three hours seems pretty quick for the server to give up on something like this.

There are a variety of possible problems here; some of which could last for longer than three hours and yet resolve themselves automatically.

In your case, it's unlikely that you are flagged as sending spam and I would certainly try to email the person again the next day, or perhaps using an alternate email address on a different domain.

Let's look at how this works and what some of the possible failures could be.

Host names and email

When you send email, one of the first steps that the sending server or mail program needs to do is determine what server on the Internet is designated to receive email for the domain.

"A typo in the domain name could cause exactly this kind of behavior."

It does this by querying the domain name system for what's called an "MX" or mail exchange record. This is very similar to the more common function of DNS where the computer might ask, "What is the IP address of this domain?" Instead, the question is more like, "To what server should I send email that is destined for this domain?"

For example, if email is destined for leo@randomisp.com, the sending email server or email program will ask, "What is the server to which I should send email destined for email addresses on randomisp.com?" DNS will respond with either another domain name, perhaps something like mail.randomisp.com, or a "not found". When DNS responds with a different name, this allows mail for a domain to be handled on a completely different server than the server hosting the domain's website.

In this case, "not found" is actually not an error, per se. The protocol is that if there is no mail exchange record for a domain, then the domain itself is used. So, if in response to our query for randomisp.com, the response had been "not found", then mail would be sent to the same server hosting the randomisp.com website itself.

In your case, the error indicates that either the server specified by the mail exchange record can't be found (i.e. mail.randomisp.com can't be found, to use my example) or the mail exchange record itself did not exist and that the domain name used in the email address was also not found (randomisp.com doesn't exist).

DNS failures

DNS can fail. By that, I mean that it is possible for DNS lookups to fail for a variety of reasons.

Some of those reasons are permanent. Perhaps the domain name has, as you theorize, not been renewed. A quick review of the domain registration using a whois service would tell you if this was the case. Perhaps the company has gone out of business. One of my first checks would be to see if you can access the website for the email service to which you are attempting to send email.

Failures can also be temporary. For example, DNS servers can sometimes go offline; they can crash or have other problems. Perhaps the data center used by the service has been cut off from the Internet for some reason. Typically, these problems are resolved relatively quickly, but for some domains and servers, that may take a while longer. That's kind of why I'm surprised that your sending server gave up after only three hours.

The entire mail system is actually built to generally tolerate delays of multiple days, not simply multiple hours.

What to do

In a case like this, it's difficult to know exactly what next steps to take. I'd try to go to the website of the email provider and perhaps check the DNS records and the domain registration for the provider. Assuming that all of it looked as it should, I would suspect a transient error.

But there's no way to know for sure.

As I said earlier, you're best bet is two-fold:

  1. Try sending email again in a day or two. Almost all failures of this sort that are truly transitory are going to be resolved within that time frame. (If it truly is a transient problem and it's not fixed within a couple of days, you might suggest to your recipient when you finally make contact again that they find another provider.)

  2. Try contacting your recipient some other way. Typically, that means using a different email address using a different email provider or giving them a phone call, and IM, or something else that doesn't rely on the domain of their email provider to work.

And for the record, I would also check to make sure that you've actually typed in the correct email address. A typo in the domain name could cause exactly this kind of behavior.

Article C4914 - August 27, 2011 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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3 Comments
Kay
August 28, 2011 4:06 PM

Leo, if you look up the URL and it says oops I can't find it....But in the Who Is search, it appears to have been renewed just recently could there be a mistake? Or could this person be blocking the email---there is no reason to think so, and so my guess is that it wasn't renewed properly.

It you may simply mean that the person who owns the domain hasn't gotten around to setting up on a server yet.
Leo
30-Aug-2011

Bill
August 30, 2011 11:42 AM

I would try modifying the "HOSTS" file located in windows/system32/ETC. The hosts file carries the numeric equivalent of URLs that you have been visiting. If you rename the HOSTS file to HOSTS OLD and then try the email again, it may just work. Sometimes spyware will change the entries in the HOSTS file to redirect the search or to confuse the user. You can also use NOTEPAD to delete all entries in the file and try it. The entries will be reinstalled whenever you access the URL>

Gabe Lawrence
September 2, 2011 12:22 PM

This is a little off-topic, but when I read Leo's first statement, "Three hours seems pretty quick for the server to give up on something like this," it made me remember one of my first thoughts years ago about the whole email process and I've always wondered if anyone else has ever felt the same way. I've never understood why email servers are defaulted to try to send emails for so long. For example, Exchange tries for 48 hours on external email and 12 on internal. Since email transmission is instant, the general user thinks all emails go through if they don't get a bouncback #like ones with a typo#. I've always felt a lot of confusion could be avoided if they would get the failed email in a minute or two rather than the server trying for days to resend it. In the USA, the postal service takes about 2 or 3 days to deliver a letter. Imagine if they waited several years (or for the sake of argument, even for just a couple of weeks) to return it because the zip-code didn't match up...that's effectively what the email system has always done, just on a smaller scale. Perhaps "back in the day" email servers DID do this and they were changed to today's defaults for a reason...can anyone expand on this?

Particularly in the early days there were definitely errors that could take multiple days to repair. The e-mail system was designed to be tolerant of those errors. Even today there are errors that can last hours if not days before they are resolved. Once resolved e-mail that was queued for that destination would then be able to be successfully delivered.
Leo
02-Sep-2011

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