This issue is reported since August 2014.
- Cannot connect to KUMOI with mail app in Mac OS X
- Become unavailable to connect to KUMOI with mail app in Mac OS X.
You can connect to KUMOI via IMAP in mail app version 6 and other e-mails software such as Mozilla Thunderbird.
Some people reported that use of "Exchange" instead of "IMAP" resolve the issue in mail app version 7.