Our domain email stopped working suddenly. Inbox or any other folders are not available for all users.

This happened after sending an email without subject. I composed an email without subject and put 22 email addresses in BCC. When I clicked send button one pop-up warned and asked for subject. I clicked on cancel hoping it will return to the email editor but the email sent successfully.

I got a reply on that email and when I was trying to send a reply on that I got IO error. I refreshed the page and found no folders available :(

Also checked one other user problem was same... no folder...

Please look into the matter what went wrong... entire things happened in few minutes.

Thank you