Exchange multiple domains

rowansc1 0

Hi everyone,

I am running Microsoft exchange 2019 and my domain root is domain.net. The mail domain for exchange is mail.domain.net and autodiscover.domain.net

I also have a additional domain added which is domain.co.uk.

When trying to connect to a domain.co.uk email address using testconnectivity.microsoft.com's connectivity test, I receive an error saying that the host mail.domain.co.uk couldn't be resolved. As shown below.

It looks like it is trying to connect using mail.domain.co.uk, not mail.domain.net. So, I tried adding either a A-Record or CNAME (not at the same time) for mail.domain.co.uk to point to mail.domain.net. This got further, but then I got a certificate issue since the certificate is only for *.domain.net.

I do have a SRV record on the domain.co.uk domain for autodiscover which works fine. Does anyone have any ideas as to what is happening here and how to resolve it?

Thank you for your help!

rowansc1 0 Reputation points

2023-07-05T15:12:18.37+00:00

For clarification, I can login to the email addresses on domain.co.uk as expected on mail.domain.net/owa fine.
rowansc1 0 Reputation points

2023-07-05T23:55:39.7333333+00:00

I think the issue may be autodiscover returning the .co.uk domain for some reason. As shown from the photo below taken from the Microsoft connectivity test.

I do have all my virtual directory's set to use the .net domain, including outlook anywhere.
rowansc1 0 Reputation points

2023-07-06T01:27:33.64+00:00

Update,

I can now use the domain.net email addresses on the connectivity checker successfully. However, if I try to use the domain.co.uk emails, I am presented with the below error:

2 answers

Kael Yao-MSFT 37,681 Reputation points Microsoft Vendor

2023-07-06T01:30:21.5733333+00:00

Hi @rowansc1

Do you have a certificate which includes mail.domain.co.uk on your Exchange server?

If not, this may be the expected behavior as the tool cannot find a valid certificate for this domain, thus the error message Host name mail.domain.co.uk doesn't match any name found on the server certificate is returned.

Here is also a thread discussing the similar scenario for your reference:

Multiple certificates on Exchange 2019 server

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rowansc1 0 Reputation points

2023-07-06T07:18:05.1133333+00:00

Hiya,

Thank you for your reply! Unfortunatly, i do not have a certificate i can use for the domain.co.uk. However, as per my last comment, it looks like I have gotten a bit further. I can connect successfully using a domain.net email address on the connectivity checker but if I try to use a domain.o.uk email adress, I am met with an 400 error from IIS7 which I don't understand.

Is there a fix for this error?

Kael Yao-MSFT 37,681 Reputation points Microsoft Vendor

2023-07-06T08:50:09.0333333+00:00

I can connect successfully using a domain.net email address on the connectivity checker but if I try to use a domain.o.uk email adress

To me this may possibly caused by certificate since domain.net is working fine.

You may need to include this domain in your certificate otherwise clients would not trust the server.

rowansc1 0 Reputation points

2023-07-06T09:11:14.4533333+00:00

Hmm, thanks :).

I'd prefer to not have to add domain.co.uk to the certificate as thats quite expensive for me. Do you know if there are any alternative methods which don't involve adding another certificate? It does seem to be connecting to mail.domain.net fine, but IIS isn't happy with a 'Exchange ActiveSync returned an HTTP 500 response (Internal Server Error).'

Full error: https://pastebin.com/JiiRaeH8

Kael Yao-MSFT 37,681 Reputation points Microsoft Vendor

2023-07-06T09:23:40.93+00:00

If you do not add the domain to the certificate, clients like Outlook would still be able to connect to the Exchange server.

However you would possibly get a pop-up like below when connecting:

which you can process Yes to ignore it.

rowansc1 0 Reputation points

2023-07-06T09:39:14.14+00:00

Hi,

I don't mind having that error. However, the connection just fails on the connectivity checker.

rowansc1 0 Reputation points

2023-07-06T21:20:33.96+00:00

The link to the full error is here: https://hastebin.com/share/hoyuqixeva.yaml

A screenshot is also below:

I've created a new account and I have re-run the test using this account. The checker still fails, but this time with an IIS7 HTTP 400 error.

Kael Yao-MSFT 37,681 Reputation points Microsoft Vendor

2023-07-07T06:29:21.6066667+00:00

It is hard to tell the cause only from HTTP 400 error.

Can you actually connect to Exchange with a mobile (since you are testing Activesync) or with a Outlook for windows client?

rowansc1 0 Reputation points

2023-07-07T13:00:29.7866667+00:00

Yeah, I've fixed the problem now. It was to do with UPN. So I added that onto the domain forest and then changed the users UPN, which now works!

Thank you for your help so far! Glad its all now working.
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rowansc1 0 Reputation points

2023-07-07T13:01:32.8733333+00:00

I've fixed the problem now. It was to do with UPN. So I added that as a registered UPN suffix for the AD forest and then changed the users UPN, which now works!

ActiveSync is particularly picky about UPN/PriSMTP alignment.
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Exchange multiple domains

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