Autodiscover looking for wrong domain

We are having the autodiscover popup show up on several different mailboxes asking to allow settings from a domain that is not ours (specifically grubhub)

Allow this website to configure facility@contoso.com server settings?
https://www.grubhub.com/autodiscover.xml
Your account was redirected to this website for settings.
You should only allow settings from sources you know and trust.

We are not grubhub.

Why would it be asking for grubhub.com autodiscover when we are not gruhub?
jjwolvenAsked:
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viktor grantExchange ServersCommented:
Hi,

Check DNS, do you have any redirection?

Normally when you have this pop up it is because you have some kind of DNS.

Cheers
Viktor

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jjwolvenAuthor Commented:
we send our autodiscover to an AWS load balancer
MichelangeloConsultantCommented:
If redirection happens for some mailboxes only it may be useful to look into the client as per following technet:

https://support.microsoft.com/en-us/help/2212902/unexpected-autodiscover-behavior-when-you-have-registry-settings-under

Some background info on autodiscovery:

https://technet.microsoft.com/en-us/library/bb124251(v=exchg.160).aspx
jjwolvenAuthor Commented:
We finally figured it out.
Old cached DNS records and hosts files that were not updated (before I started) had information from an old business arrangement to an alternate CNAME.
That CNAME no longer exists, and the IP has been allocated to the other company that was coming up.

Cleared out Exchange cache, DNS cache and cleanup hosts record and it working fine now.
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