This could happen on systems which have used Exchange but have changed back to POP3 E-mail delivery. Checking the to-be-sent messages is the key, remove the adresses that are exchange adresses and substitute them with the real POP E-mail adresses.
Error 0x80040201 in Outlook appeared after trying to send new mail to SOME of recipients! I suppose, that were recipients, who already recieved some mail while I was using EXCHANGE account to send them.
NOTE: I have no addresses in my outlook adressbook! But while creating new mail and typing some email address Outlook get it from, IMHO, send folder =) I.e. mail sent over exchange accout!
NOTE2: You are able to view some properties by right-button-clicking on address (name) in the „TO:” field. When I did this, I recieved in one case and Error (something about „can’t find object), in other case a windows „Message properties”, where field „Email type” was set to „EX” (instead of „SMTP”)
SO! The solution is – to change recipient properties and set EMAIL TYPE to SMTP, and EMAIL ADDRESS to something like „(E-Mail Removed)” and do not use auto-substitution of recipient, or DELETE cache record in pop-down list by pressing UP, DOWN and DELETE button on keyboard and then typing email again…
The other way is by opening the profile folder and deleting the .nk2 file.
* Open up windows explorer, and paste the following into the address bar: %APPDATA%\Microsoft\Outlook
* Delete the Outlook.NK2 file that you find in this folder.
* delete all NK2 files