My boss has a new iPhone8. I've set him up to access the IMAP server at the office. Inbox works just fine and he can send messages. The problem is that the Sent and Trash folder on the iPhone do no synchronize with the server. Apparently, this is not an uncommon problem since I've found lots of posts about it. However, none of the instructions I've found so far seem to work. How do I do this?
The mail server is Dovecot IMAP. The iPhone is using the normal mail facility, nothing special or 3rd party. The selected server setup is 'Other'. Inbox synchronization works. Messages deleted on the iPhone, and sent messages are not synchronized with the corresponding folders on the IMAP server.