Undeliverable Mail

[LordLuciendar]

It's been three months of banging my head against the wall with this problem, I figured I'd throw it out to the community to get some new eyes and ears.

I have a business client who works very closely with the military and law enforcement. They have a network which spans multiple sites with a few dozen systems. On one computer, and only one computer, they experience intermittent periods of sent mail to address at .mil domains being undeliverable. I have now personally checked, double checked, and checked yet again all settings in the computers networking and Outlook configuration. The message we receive is:

Your message did not reach some or all of the intended recipients.

Subject: Updated reprort
Sent: xx/xx/xxxx xx:xx PM

The following recipient(s) cannot be reached:

'xxxx.xxxxx.xxx@xxx.mil' on
The recipient has been deleted or has no e-mail address.

The single computer with this issue, is the founder and CEO of the business, and he's rather cross that nobody can resolve the issue. Not a single member of his staff experiences this issue, even when corresponding with the same email address as is reported undeliverable on his system. We have confirmed, and confirmed again, with the email service provider that their DNS servers contain the correct records for the .mil domains in question.
He has also mentioned that this issue previously occurred with Eudora, and that it continues to occur with both his standard email and his federal law enforcement account with the exception of when he logs into the federal law enforcement account via VPN and webmail.

There is nothing I can think of which would cause this issue. Any thoughts? ACL on the .mil mail server... any ideas... I'm fresh out.

 

[hang-the-9]

Have you tried having him using a different computer but with his user account? Is it following his account? Does that email address need any type of encryption which his PC may not have? Aside from checking the computer, have you checked the email server logs?

 

[Ijack]

It just doesn't make sense. The report is coming from the remote server and says the address doesn't exist. That means it is passing through your SMTP server but being rejected at the other end, which would seem to rule out anything to do with the sending user or computer.

The only solution that I can think of (which you must have already checked) is that he is typing the address in wrongly. Is he picking it from an address book, or typing it in anew? It might be worth trying typing it in rather than picking it from an address book.

If the error were anything other than "invalid recipient" then I might suppose that it could be a blacklisted IP address. I suppose it's just possible that the remote server retuns that message whatever the true error.

I shall be intrigued to hear the answer.

 

[LordLuciendar]

We've gone over the email addresses a few dozen times, they are typed correctly. Furthermore, the properly formatted, correct, email address shows up in the error message we receive, confirming that it is formatted correctly and is correct.

I agree that it doesn't make sense, the remote server is issuing the response we are receiving, which seems to eliminate any settings on the local computer. That and we've verified a half dozen times every network, DNS, and outlook setting. He reports that the issue he experiences occurs through webmail as well (Time Warner Cable). I have had him test webmail over the phone when diagnosing the error to the same result. The most strange thing is that 50% of the time he has no issue sending to the exact same email, either through Outlook or webmail.

My current hypothesis is this:
Every email I've ever received from his staff is from his corporate domain, indicating that they are most likely using his corporate mail server to send and receive email. His address at Time Warner Cable may be unique in using the Time Warner Cable mail server. He also experiences this error when sending email from his federal account through Outlook on his local computer, it might be a stretch, but the federal mail server may be unreachable when not connected to VPN, thus emails sent using his federal account may attempt to use the Time Warner SMTP server to send, hence the identical error.
This all points to the possibility that the Time Warner mail servers may be blacklisted by the .mil mail servers intermittently. I have contacted Time Warner technical support, including having the regional director on conference call. They consistently are unable to resolve this issue, even after admitting to receiving the emails and errors on their end. The only reasonable solution I see would be to have him migrate to an email at his corporate domain.

Now for some careful wording to see if I can convince him to do this.

 

[Ijack]

I think your hypothesis and solution must be correct. I'm sure that if you can convince him that's it beyond your control then you ought to be able to get him to change. But it can be difficult when it's the CEO - sometimes they expect the impossible.