Gmail has limitations

Gmail has increased the limit of attached file size to 20MB, and overall the storage space to 6 GB. But, did you know that there is a daily quote on sending mails? Breaking the rule will cause Google to disable your Gmail account temporarily without any warning.
Lockdown in sector 4!
Our system indicates unusual usage of your account. In order to protect Gmail users from potentially harmful use of Gmail, this account has been disabled for up to 24 hours.
So, there are some rules that you should obey in order to avoid temporary shut-down of Gmail.