any host will impose a limit on the number of emails that can be sent in a given time.
It's not a question of whether the users have consented to you sending the email, the host has no knowledge of any such agreement, that is between you and your website visitors.
the host is just trying to prevent spammers from abusing the email server.
Think in terms of speed limits. I know I can drive safely at 75mph, but that doesn't mean the teenager who just got there license can. The limit is set at 55mph, not because of my personal abilities, but because of the general populations abilities and what is considered safe for all.
I think with the limit fasthosts has of 15 - 20 in an hour, you will have difficulty getting a mass email script working.
If you had 100 emails in the database, you would need to leave the script running in the browser for 5:30 hours to send all of the emails.