Using New Outlook on Windows for professional communication and productivity
This issue is still happening for me. I did notice one or two messages earlier in the week did send ok when I was replying or forwarding a message but the vast majority have failed to send. I do not have problems sending new emails, it's just the replies and forwarded content that poses a problem as reported here by other users.
Ironically whenever the taskbar alerts me to knew messages in this thread, if I click on one of those alerts it conveniently opens the older 'Windows Mail ' which works much better than Outlook. Shame MS don't ditch Outlook and go back to Mail, at least they fixed 99% of the bugs in that.