I found a strange bug that happens 2/3 times already.
I will try to explain it clearly (not an english person).
When I send a email to Bob with an attachment and a content, it works correctly.
Now when I go back to my Sent folder in Outlook, to find this email to resend it (because I want to change something), I click on Forward.
I put Bob email address. I remove in Subject FW: to have the same subject as my first email.
I remove the attachment, and then attached it again (I want to send a new revision for example, with the exact same name).
I remove or add a line in the body of the message.
When I send it, Bob receive the previous version of the email (the first version) with the old attachment and the old text.
The new version of the email is attached in a .dat file.
It is not clear to me what is happening, but I guess the bug can be serious.
It only works if I send the email to the same person, and if I delete and reattached the doc or ppt file for example.
I hope you have enough details.
The OS is Windows 10 with Outlook 365.
If you need more information, I can reproduce the bug again and maybe find additional details that can be useful.
Thanks for your help.
EDIT: I did some additional testing.
To have the bug you forward the email to the same person, you remove the attachment and you reattach it (same name), and you remove the FW: in the subject to have the same subject as the previous email. It should trigger the bug