View Full Version : E-mail Server Tech Question

29-02-2004, 10:09 AM
A fairly "deep" technical question about e-mail
servers. (Deep for me, anyway!)

If I send an e-mail and have one character wrong in
the individualís name (i.e. not in the domain name),
e.g. matthewk@fiction.com (two Tees), the correct
address being mathewk@fiction.com (one Tee), my
understanding is that such an e-mail will get "out"
OK through my ISPís (originating) mail server
(because it sends to a valid/registered domain name,
not to an individual) and "in" OK to the intended
destination domain mail server. Once there, however,
the destination mail server will check the individual
name, determine that it is invalid, then reply/return the
message with a system-generated delivery failure
notice, with some comment like "Sorry, no mailbox
here by that name."

However, if I get the domain name wrong, my ISPís
mail server will detect this, and, without even
attempting to on-send my e-mail, will auto-generate a
reply/return the message to me with a system-
generated delivery failure notice like: "This address
has permanent fatal errors."

I hope Iíve described that well enough that the
questions are clear. How close am I to being correct
in my assessment?

29-02-2004, 11:04 AM
Thats how it works for me.

Anything sent to my domain gets through. Then its up to me to decide what to do with it. Some domains may contract with the ISP for "mail bagging" services, which could modify this behaviour?

Anything with an incorrect domain doesn't come to me, and if the domain does not exists you get the ISP return.

29-02-2004, 12:16 PM
Yep that's how it works your ISP will valiadate that the mail can be sent to the domain name but the user address is handled by mail server.
If it's a hotmail type or ISP mail account then that server will respond for corporate accounts you will recive a message from that server. However sometimes you can set up alas's for common misspellings of particular users so your mail will get through anyway.
There are a few other things to consider - sometimes a company will block mail from a particular domain or ISP as it may be spam or reject mail with certian attachments such as large images exe etc.

29-02-2004, 12:20 PM
What do you mean by: "Some domains may contract with the ISP for 'mail bagging' services, which could modify this behaviour?"

This is something to do with the relationship between a domain+server (one thing: right?) and the means by which it connects to the web?

29-02-2004, 12:29 PM
This is not idle curiosity, but checking on something told to
me by someone else. And that 'something' just didn't
sound right. Here's what was proffered as an
explanation for a 3-4 month delay in receiving
an e-mail delivery failure response. Based on what
contributors here are saying, I think a reality
check is needed by the person who sent this, or the
IT manager who told him this . . .

"The delivery failure receipt for the e-mail you
sent to DeeKnee is controlled by your Internet
Service Provider and is not a function of our
systems. As the IT manager explains it to me it is
your ISP that is endeavouring to deliver the message
and therefore needs to notify you if it is unable to do
so. The delay is unusual but we are unable to explain

That communication came from another
person at the same domain name, so I know that the
earlier failures were because I spelled DeeNee
without the "K"

However, four months to generate a "no mailbox of
that name" type response?!?!? (A quasi government
department, unfortunately)

Anyway, on the basis of comments so far, the
explanation (italicised, above) given doesn't seem
to be valid, does it?

29-02-2004, 12:38 PM
> What do you mean by: "Some domains may contract with
> the ISP for 'mail bagging' services, which could
> modify this behaviour?"

If I contract with say, clear.net to handle my mail for my domain, I could also allow them to test for valid users @ my domain and contract as to how invalid emails were processed by them (i.e. dumped, returned or forwarded). My reference to "some domains" is to the owner of those domains.

These are commercial issues agreed by the parties involved and could affect the behaviour that you may expect. There is no hard rule in those cases, and any agreements are commercially sensitive so you will not find out from the ISP. Just as some domain owners may dump all unrecognised user addressed email and not have it vetted by their postmaster. You will never know.

Graham L
29-02-2004, 02:16 PM
The domain name is checked. It is sent to a DNS server . Only if the spelling matches that of a host in the hierarchical DNS will the mail sender get an IP address to send the mail to. It might not be the right destination (depending on your spelling) , but it will be a valid destination.;-)

What happens at that destination depends on the way the mail processing software has been configured. Some send any mail with unknown addressees to a "postmaster", who will see what can be done. Whoever is lumbered with the postmaster alias usually has other, real, work to do. Some systems(most, these days, with spam and other junk?) will bounce it with an appropriate error code. I suppose it depends on how important incoming mail is considered. You might want to handle customers carefully.;-)

29-02-2004, 02:57 PM
Looking at the "bounce" server response, this is what it said:

This is an automatically generated Delivery Status Notification.
Delivery to the following recipients failed.

I had spelled only the mailbox name incorrectly. The domain name was correct. So, it is possible that my wrongly addressed e-mail languished in the "postmaster's" mailbox, until it came to the top of the to-do list, right?

But - no matter what - such was not a function of my ISP, was it? It was a function of the destination domain name server/administration or that domain name's ISP, depending on the contractual arrangements that had been set up - right?

Graham L
29-02-2004, 03:37 PM
That would be handled by a not-found redirect to Postmaster, with a daemon which runs every so often to bounce any which get there. It's definitely not your ISP. It might be the the mailserver of the ISP of the destination; it might be a mailserver owned and run by the destination.

29-02-2004, 03:40 PM

Even if I struggle just a little with some of the other concepts
I can be sure that it is not a function of my ISP.