Hi, I hope there is one kind soul out there that are able to help me resolve this issue for a user in my organization. This is the last resort as I've been doing quiet a lot of testing to get this sorted out. Case: - Using Outlook 365 - Have successfully added the e-mail to Thunderbird through IMAP settings - I can successfully send and receive e-mail on both desktop and mobile (using Spark on iOS) Problem: - When I send an e-mail on desktop, it is added to "Sent" folder on mobile. - '''HOWEVER, the issue is when sending an e-mail from Spark (iOS), it is not seen on the "Sent" folder on desktop where Thunderbird is used. What could be the cause of this happening?''' What I've tried: - Testing a lot of different settings. This is the only settings where we can both send and receive e-mail on: IMAP: outlook.office365.com / SSL TLS / OAuth2 / Port 993. SMTP: smtp.office365.com / Port 587 / OAuth2 / STARTTLS - Removing and adding account more than 10+ times - Made sure, under "Synchronization and Storage" in TB, that the top checkbox is checked (Keep all messages in all folders for this account on this computer) I might also tell you that syncing works perfectly for everyone else, however, they are using Outlook on both mobile and desktop and using the office 365 login option. Which Thunderbird does not have. Anyone have any ideas on what I could test or try in order for iOS and Thunderbird to sync sent msgs properly? That is, sending emails from Spark on iPhone and getting them to the Sent folder in Thunderbird on desktop.