[Evolution] Persistent "Error while sending message" due to malformed recipient address

[Vidar Evenrud Seeberg <web infosikring no>]

Hi gurus!

Ubuntu Gnome 17.04
Evolution 3.22.6
Account using Evolution-EWS

I wrongly placed a space in a recipient's email address. Now I get 
"Error while sending message. At least one recipient isn't valid., 
Recipient "<address>" isn't resolved. All recipients must be resolved 
before a message can be submitted" when I manually check mail. I also 
get a message reminding me of unsent messages exists when quitting 
Evolution. The problem is I can't find the problem message anywhere so I 
am not able to correct or delete it. The Outbox folder is empty, so is 
the Drafts folder.

Please help!

Best regards
Vidar