Office 365 (Known Issue) - One or more folders is named incorrectly
If you receive the error message "The name of one or more of your folders includes the character "/" or more than 250 characters. Folders with names that include this character can't be downloaded to your IMAP e-mail program. Please rename these folders: <name of folders>", please follow these steps to attempt to resolve the issue:
Some clients are receiving an error message that one or more folders in their mailbox is named incorrectly.
Please delete the problem folders and then empty the trash. Note: Emptying the trash is important.
Most problems involve calendar folders so not only look for problem folders in your email folder list but also in the 'Calendar' tab.
If you still receive the error message after deleting your problem folders and emptying the trash, please look once again for problem folders. The emails will have the name of the problem folder(s).