Two of three accounts with this error 554 5.1.8 Email Outgoing Blocked

Two of three accounts with this error 554 5.1.8 Email Outgoing Blocked

Hi,

Recently two users try sending mails from portal mail web and don't is possible by this error (554 5.1.8 Email Outgoing Blocked) and uin the bottom of screen appear a menssage: This account is bloqued for security reasons. I try change status in admin panel but a message said: This option is only disposible for pay users.

I don konw why this happening.