Using older versions of Outlook for Mac for personal email and calendar
For the last 2+ months this issue has been driving me crazy and it's definitely unacceptable that Microsoft has yet to provide a fix for such an important issue.
Over the timeframe I have been encountering this issue, I've been stalking this message board and appreciate everyone's input and workarounds. Like many others, I have been composing my emails with attachments in the app, saving in drafts, and then eventually sending from the web version. I've tried installing both beta and regular updates, but nothing ever seems to be consistent.
With that being said, one of the more recent previous posts mentioned the possibility that Add-Ins could be causing the issue -- Particularly the HubSpot integration. Over the past few days, I have removed the HubSpot Add-In from my Outlook desktop app and this has worked like a charm. Since removing this and restarting the app, I have not had any problems successfully sending emails with attachments from the desktop app.
As a result, for those of you that have the HubSpot Add-In installed on your desktop app, I would recommend giving this a try to see if it works for you!
...knowing that we have all been through with this issue, it also wouldn't surprise me if I suddenly start having problems again :)