Moving off a self hosted Dovecot server to Office 365. The mail store is Maildir: each folder has cur, new and tmp subfolders full of individual message files with long random names.
About 60,000 messages across 40 folders. How do I get this into Outlook or straight into 365?
Each file inside cur and new is a complete RFC 822 message, so the data is clean, it is just packaged in a way no Microsoft product reads.
At 60,000 messages skip manual tricks and use a converter. SysTools Maildir Converter takes the Maildir root, reads cur and new, ignores tmp, maps the dot prefixed folder names to a normal folder tree and writes PST files you import into Outlook or upload to 365 with the network upload method.
The manual alternative for a small mailbox is renaming message files to .eml and dragging batches into Outlook folders, but at your scale that loses folder mapping, chokes on the thousands of files per drag and takes days. Not worth it beyond a few hundred messages.
One thing to verify after conversion: Maildir flags live in the filename suffix after the colon, S for seen, R for replied. A good converter translates these to read and replied status in the PST. Spot check a folder to confirm read states carried over.
Converted all 40 folders, read states came across correctly. Uploading the PSTs to 365 now with the network upload tool.