Error 441 - Account is at / over data quota
Description of problem
Each AuthSMTP account has a monthly data and message quota that cannot be exceeded without upgrading, error code 441 means that you have used up all your data transfer quota.
If you send an email to one person containing a 1 megabyte file it will use up between 1 and 1.5 megabytes of your data transfer quota - if you are unsure what your data quota is you can view your account quota limits via the control panel.
How to resolve this problem
If you need to send further emails before your monthly quota reset date you will need to upgrade your account, you can upgrade permanently or just on a one-off basis via the control panel at any time.