Although Mimecast can connect to the journal mailbox and authenticate, occasionally the message extraction failed due to a message blocking the queue.
Once you've confirmed that no infrastructure or device changes have been made, or if there are any known issues that may prevent the successful extraction of journal information between the Mimecast and the remote infrastructure, consider if the journal mailbox contains:
- Large items that might cause a timeout during extraction?
- Any items that do not hold a message envelope (when using Exchange Envelope Journaling)?
If you find messages that might be causing the issue (most likely the oldest items in the mailbox), move them to a subfolder of the Inbox and report this to Mimecast Support. Mimecast can test extraction and hopefully continue extracting messages successfully.