Obviously it isn’t possible to export a mailbox of appr. 7.6 GB data and appr. 48k emails into a mbox file. The beachball spins for a while. But no file is being written until the beachball disappears.
Is there a solution or a workarround in order to get a mbox which could be imported into an IMAP server?
Hold the Option key and choose Help > Report bug to start a support ticket.
When the application is stalled, do a Spotlight search for Activity Monitor . Select our application in the list of processes - it should show “(Not Responding)” and the name in red - and press Command-Option-S to run a sample on it. When the sample window opens, press the Save button and save it to your Desktop. Please attach this text file to your Support Ticket so we can inspect it.