@kkerr1 thanks for reaching out about this and sorry to hear that you're having this problem.

@exextoc are you able to provide input on this issue?

We are aware of this issue. We responded to the StackOverflow post. We have engaged the Outlook team to address this information. We don't have an ETA for fixing this issue. The workaround is to host the files elsewhere.

Is there an update on this issue? It's 7 months on, and I can still replicate the issue. The answer of "use a service that has more relaxed security" isn't a great workaround to have in place for this long, especially when it can involve customer data.

We are now seeing this in the latest semi-annual releases 1902 and 1907 monthly releases. This means that seven months after reporting this issue, it has expanded to both public release channels. Without a fix we will have to build a workaround to address. @exextoc and @kbrandl This is extremely disappointing and the second time a bug has required a substantial workaround on our end in the last few months. The other being #433. Is there a better mechanism to escalate these issues?

@kkerr1 thanks for reaching out about this, and sorry to see that the team's progress has been so slow with this issue -- I can certainly understand your frustration.

@wamaina FYI (for escalation, since you're currently on rotation.) @exextoc can you please provide an status update on this issue (including an ETA for resolution, if available)?

Can we get a status update on the status update?

@exextoc any update on this issue? It's coming up to a year since opening, and almost 4 months since a status update was asked for.

Sorry for the enormous delay on this, this is unfortunately not something that our team directly owns, so that's why, mostly, the delay.
We recently ship an attachments API (in our 1.8 release) that enables you to add a base64 encoded attachment, have you tried this? here is more info https://docs.microsoft.com/en-us/office/dev/add-ins/reference/objectmodel/requirement-set-1.8/office.context.mailbox.item#addfileattachmentfrombase64asyncbase64file-attachmentname-options-callback

the fix for the original bug is still pending and might be delayed a bit more. no specific ETA.
thanks for your patience.

Thank you @JuaneloJuanelo . We have tried that API, and it does fix the issue, but as far as I know 1.8 is still in preview and not GA. Do you have an expected timeline for GA?

1.8 is GA now! it was announced a couple of weeks ago (@ignite!!)
Starting on: Windows: 16.0.12130.20272 , Mac: 16.31 November Update, Online November

Oh great, thank you @JuaneloJuanelo . That workaround is sufficient for us then.

This issue has been automatically marked as stale because it is marked as needing author feedback but has not had any activity for 4 days. It will be closed if no further activity occurs within 3 days of this comment. Thank you for your interest in Office Add-ins!

This issue definitely cannot be closed. Although a workaround is present, the original issue still exists, and as far as I know not even the documentation has been changed to indicate the old API doesn't work.

As pointed out in stackOverflow, but adding this info here just as reference, this is an Outlook bug, exactly the same situation happens when using Outlook manually. This is not in the Office Platform.
As soon as the bug gets fixed in Outlook, the API will work as usual, as a workaround please use the attachments API.

Given that

a. this is not an issue on the Office Platform team and
b. Outlook team is aware and working on a fix (internally tracked with 2599582) and
c. there is a workaround using the new attachments API.

I am closing this issue.

We have fixed the bug and the fix should be available in build 16.0.12625.10000 or later. Depending on the release channel you are on, getting an updated build can take anywhere from 4-8 weeks.