They are making changes to how many recipients someone can send to in 24 hours. If they exceed the recipient count for the day, they will need to wait till the following day to be able to send or upgrade to a higher account.
Lite: can share/send to 25 email address
PRO PLUS: can send/share to 100 email address
Ent: can send/share to Unlimited email address
Limits had to be made because some users were using our service to send out spams, and causing mail clients to block our notifications.
They will see these error message if they have reached their quota: