The full mail policy for shared servers can be found here: http://www.hdwebprovider.net/clients
There is a 500 hourly email limit per domain on all shared servers. This limit is also applied towards mailing lists. If you send over this amount in any hour, the e-mails will fail and may bounce back with a undeliverable error.
Shared servers limit each connecting IP to 30 POP checks per hour. If you go over this, you will likely get a password error indicating your login is incorrect. To fix this, just wait an hour and it will automatically unlock. To prevent this from happening, disable automatic send/receive or set a higher time interval, such as checking once every 10 minutes.
Dedicated server accounts can send and receive unlimited emails per hour.
You get a bounce back indicating your email has been tagged as spam due to exceeding a 500 e-mail per hour limit.You will need to wait until the next hour to continue sending emails.
If this problem does not go away by the next hour, please email email@example.com
Online businesses that use e-mail marketing must be careful to follow all the CAN-SPAM rules.
All recipients must have opted in.
An unsubscribe mechanism must be included.
Your physical postal address must be included.
Deceptive subject lines and false headers are outlawed.