SUMMARY
When send later agent is used, the sended message in not stored on the sent folder of the account used. Instead you have a copy stored in the local folder.

STEPS TO REPRODUCE
1. Have at least 2 different indentity, using different sender : for example one google and one your provider
2. Use google identity to start a new message sended to your second email
use the send later (optionnal via google smtp service) and use 10minutes to one hour later option
3. Once the email is sended by kmail2 look at Sent folder on your google account, the message is not there. 
4. Open local folder Sent you will find the wrongly stored message here.
5. Open local and sent google message header and you will see the same id for identity and Transport. Like for example in my case
X-KMail-Identity: 948660293
X-KMail-Transport: 464288440
X-KMail-Identity-Name: BF Gmail
X-KMail-Transport-Name: smtp.gmail.com

Kmail2 has all the informations to store the sended message to the right folder (Sent of the Identity, in my case)

Notice : this deviant behaviour has been seen this year if my memory is right. I didn't got this trouble before. 
Sorry for the quantic precision ;-)


OBSERVED RESULT


EXPECTED RESULT


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION