As outlined in the [Microsoft documentation](https://learn.microsoft.com/en-us/javascript/api/manifest/appdomain), trusted domains must be explicitly declared in the Office Add-in manifest using the <AppDomain> element. A trusted domain allows:
- Pages, routes, or other resources in that domain to be opened directly in the root task pane on desktop Office platforms (note: this does not apply to Office on the web or dialog APIs).
- Pages in that domain to make Office.js API calls from IFrames within the add-in.
We are currently developing a first-party native Excel Add-in as part of a strategic partnership. However, our architecture requires support for customer-specific subdomains, such as:
```
<AppDomain>https://customer1.company.com</AppDomain>
<AppDomain>https://customer2.company.com</AppDomain>
<AppDomain>https://customer3.company.com</AppDomain>
<AppDomain>https://customer4.company.com</AppDomain>
```
This list is dynamically growing, making it infeasible to maintain a static list of subdomains in the manifest. Each manifest update would require re-submission through AppSource, creating significant operational overhead and slowing down delivery.
Because of this limitation, we’re forced to distribute customer-specific manifests and rely on M365 tenant admins to install the add-in manually—introducing friction and reducing discoverability for users.
We propose enabling wildcard support for <AppDomain> entries in the manifest, e.g.:
```
<AppDomain>https://*.company.com</AppDomain>
```
This would allow all subdomains under company.com to be trusted without requiring individual enumeration, simplifying deployment and scaling while preserving security.
This limitation has been highlighted and highly upvoted by the developer community in the following feature requests:
- https://techcommunity.microsoft.com/idea/microsoft365developerplatform/add-in-manifest-allow-wildcards-for-app-domains/4162573
- https://techcommunity.microsoft.com/idea/microsoft365developerplatform/support-wildcards-for-appdomains-in-office-add-in-manifests-to-support-sub-domai/2312326