Add-in failing to load in OWA/New Outlook in Office attachment preview window

[krzysztof-plutoflume]

Event-driven Outlook add-ins fail to load when the user composes a reply using a standalone Word/Excel/etc attachment preview window inside Outlook on the web and New Outlook for Windows.

What's particularly unfortunate is that if there's an add-in that specifies an on-send handler (ItemSend), then the failure to load the add-in prevents the user from being able to send the email.

Your Environment

• Platform [PC desktop, Mac, iOS, Office on the web]: Windows desktop, also Office on the web
• Host [Excel, Word, PowerPoint, etc.]: Outlook
• Office version number: Microsoft Outlook Version 1.2024.911.200, Client Version 20240913004.12, WebView2 Version 128.0.2739.79
• Operating System: Windows 11
• Browser (if using Office on the web): Google Chrome

Expected behavior

Add-ins load correctly when composing a message from the attachment preview window.

Current behavior

Add-ins fail to load when composing a message from the attachment preview window.

Steps to reproduce

1. In New Outlook or OWA, find an email in the inbox that contains a Word attachment.
2. Click on the Word attachment to open an attachment preview overlay.
3. In the top-right of the overlay, click "Open in new window" to pop the attachment preview out into a new window.
4. Click "Reply" to start composing a reply.
5. If there was an OnMessageCompose add-in handler registered, it won't execute. If there was an ItemSend add-in handler registered, sending of the email will fail.

Link to live example(s)

Provide additional details

Screenshot of the relevant window in New Outlook for Windows:

Context

The issue prevents users of our on-send add-in from sending emails when using the described workflow.

Useful logs

I didn't find any obvious error logs in the developer tools console.

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[shighosh-msft]

Hello @krzysztof-plutoflume, thanks for sharing the detailed repro steps. It is not a repro on our side though. Can you please confirm if the add-in you are using working correctly in the regular scenario ie. a regular new compose or reply to a message?

Also, it'd really help if you could share a minimal version of your add-in that repros the issue. You can create a private github repo with the files and share with us.

[krzysztof-plutoflume]

@shighosh-msft Thanks for looking into this!

Yes, the add-in works correctly outside of this one specific scenario.

I've created a repo https://github.com/krzysztof-plutoflume/office-js-issue-4913 where I included the source of a minimal add-in, credentials to a mailbox that has this add-in sideloaded, and a video recording of the issue. I've shared the repo with you and @exextoc.

[shighosh-msft]

Hi @krzysztof-plutoflume, thank you so much for sharing all the details. I did try to repro the issue with the test account you shared. But the ItemSend seems to work perfectly every time with the test account. Can you please confirm once if you're still seeing the issue?

[krzysztof-plutoflume]

@shighosh-msft Yes, I've tried again just now but I'm still seeing the issue.

I just want to emphasise that you need to pop the attachment preview dialog out into a new window. That is:

1. Click on the Word attachment in the inbox read view.
2. In the top-right of the dialog that opened, click on "Open in new window". This should pop the attachment out into a new browser/Outlook window.
3. Only now, in this popped out window, create a reply and try to send.

The ItemSend event does trigger to some extent — there's some indication that the add-in is loading, but I don't think the add-in source is actually requested and the event times out after a while. The OnMessageCompose event doesn't trigger at all.

[shighosh-msft]

Hi @krzysztof-plutoflume, thanks for clarifying. We are able to repro with your test account and opened a backlog item to fix the same. Internal tracking id: 310221