Fixed! If you are seeing this issue, close and re-open Outlook!
Kinda stumbled upon this the other day when sending a text file through Outlook. The recipient informed me it wasn’t received. Oh jeez, did I just think I sent that?
So I sent it again and even included a pic of it attached to ease my embarrassment. Nope, the recipient was still not getting it- just the email itself.
I checked my sent items and sure enough, no paper clip icon. So I ran a bunch of tests sending different sized text files, and as you can see from the results (with my clever subject lines – sigh), some went through, some did not.
Message tracking in Office 365 revealed nothing unusual.
I wondered if it was just me, so I did a little searching and found someone reporting the same issue in the TechEd Forums:
At this point, it appears to affect only text attachments over 4MB using Microsoft Office 365 Pro Plus C2R Outlook 8431.2079 and above, but not Outlook on the Web ( OWA) or whatever it’s called now. Your experience may be different.
As you can see, I’m using the latest and greatest version!
I have also reported this issue, so hopefully it will get fixed soon.
In the meantime, compress that text attachment to below 4MB, upload to OneDrive or a shared drive.