I am the technical lead at a small startup that provides a video library to corporate clients, with a Microsoft (.net/IIS) stack. One of our features is providing each client with its own subdomain based on their username (client.oursite.com). In the past, we were manually setting up CNAME records for each client, however, it was getting impossible to manage, so a couple months ago, I added a wildcard A record (for a unique IP), bound that IP to the site in IIS, and handled any custom logic in the application. Everything has been working very well with this setup. However, I received an email from the company hosting our exchange server, asking us to remove the A record as they said it would cause issues with outlook. After several email exchanges, I received the following

We are providing hosted Exchange services to our clients. What that effectively means is that all of our hosted Exchange clients are not a part of our Exchange AD organization. The only way to support autodiscover in the hosted scenario by Microsoft is to have properly configured SRV DNS record in place which all of our hosted Exchange customers do have. For this setup to work A autodiscover record must not be present in the DNS at all.

I have no expertise in email administration, but I find it hard to believe that no one has ever used hosted exchange while having a wildcard A record in their DNS. All of our MX SRV records are correct and point to the email host's ip. Furthermore, there's no way we can go back to manually adding CNAME records. Is there any workaround here?


First, MX records are not SRV records.

Second, he's absolutely right. I deal with this issue quite often with one of my clients that also hosts Exchange for their clients. Outlook needs to find autodiscover information that points to the Exchange server. The problem with having a wildcard record is that it causes autodiscover.domain.com to resolve to your web server, which prevents Outlook from finding the autodiscover XML file and connecting to Exchange, which is why your email host is asking you to remove the wildcard record.

The workaround would be for you to host the autodiscover XML file on your web server (HTTPS root domain query) as related in the linked articles. As you can see in the articles, there's a definite order of operations that Outlook uses to locate the autodiscover information. You can see in the articles that the third discovery method is the one that your wildcard is causing problems with (HTTPS Autodiscover domain query).

The fifth method is the one that your Exchange hoster is using for their clients.



  • Thanks this was the workaround makes sense. btw I realize srv and mx records are separate, and I put a slash between them, but i guess the text editor stripped it out... – Daryl1976 Jul 19 '15 at 0:10

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