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We run exchange, but all our emails are routed through a 3rd party mail service, which filters, scans etc.

We have 3 domains that we receive email on, lets call them ADomain.co.uk, BDomain.co.uk and CDomain.co.uk.

We own and look after the domain names. But we pay a 3rd party company to host the websites and just point the domain names to the websites.

There is a webform on one of the websites adomain.co.uk, that can be filled in, it should then post the details of the form to us at webform@adomain.co.uk, however we never receive that email.

If they change the address to point to any other address like a gmail or hotmail address it works.

If I email the webform@adomain.co.uk address from a different external account it works, but the email from the hosted site to any of our domains, a, b or c, never comes through and our mail host has no record of a connection attempt being made.

By changing the user account that it sends from to a gmail account we finally get a NDR:

Mail Delivery System

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:

webform@adomain.co.uk No Such User Here

The email address (and we've tried several, at all 3 domains) is correct. Noone else has any trouble emailing the domains. the hosting company have no trouble emailing anyone else other than us. Can anyone explain what's going wrong?

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This is a classic problem, and it is the hosting company that has the issue - you need to get them to fix it.

Basically most web hosts will be setup to presume that you are using their services for everything - which includes email. That means when you send an email from one of their systems, it never even attempts to connect to a remote system, it uses their internal email server only. The NDR you have seen isn't an Exchange NDR.

The web host needs to remove the references to the domain from their internal systems so that email is not routed internally, but it uses the public DNS records. If they will not, then you need to use a different web form that can have an SMTP server hard coded. I would then suggest that you setup a new DNS host for the web form (web-smtp.example.com) which is pointed to your Exchange server directly. Add in a restriction on the Exchange server or firewall (wherever you are restricting SMTP traffic) to allow the web server to send you email.

To repeat - this is NOT something that you can resolve yourself without changing the web form. It is a configuration done by the web hosting company.

  • Thanks for the help, I'm working with them now to get it resolved. Makes perfect sense. :) – SysAdminUK Mar 15 '17 at 10:13

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