Frontier Mail problem

[Time Planet News]

Frontier Mail problem Today, using Thunderbird, I sent out about 16 emails--not an unusual
number, although several were to myself (emailing Amazon webpages for
items I'm interested in). But suddenly I can't send any more from my
Frontier Mail account. I'm getting the error message "An (SMTP) error
occurred while sending mail. The server responded: 4.7.1 <DATA>: Data
command rejected: x...@myfrontiermail.com exceeded daily messages threshold."

Any thoughts on what could be wrong? I checked the Frontier Postmaster
webpage
https://postmaster.frontier.com/error.html

and couldn't find this error code--although I did find "Message rate
limit exceeded
Error Message: 452 <[IP address]> exceeded hourly message threshold
Error Message: 452 <[IP address]> exceeded daily message threshold
Solution: Check your machine for viruses or trojans; your computer
may be sending out spam without your knowledge. Reduce the amount of
mail you send per hour or per day. Business class service has higher
limits than Residential; if you need to send more mail as a business
requirement, consider upgrading."

--
Thank you,
Jo-Anne