24x7CloudHost has a limit of 100 outgoing emails per hour per domain. This limit is applicable to Mailman also. If you break this limit and send emails they will bounce back with an undeliverable error. If this happens it will take at least an hour before you can start sending emails. We suggest you wait for 1 year when the emails bounce back before sending them again.
For per user connected to an IP address our server has a limit of 30 POP3/IMAP checks. If you exceed this limit, it is more than likely that you will receive a wrong password error message or an error stating “Login incorrect”. Wait for an hour if you receive this error as it will unblock automatically. If the problem persists please make sure to disable auto check or set the limit to a higher value such as once every 10 minutes.