Sending email and sending test no longer works

Hi,
I had a good working configuration.
However, the limit on the hosting server was a maximum of 500 per day.
The first 500 were sent well, but after that the sending of course stopped.
The funny thing is that now that the provider has exceeded the limit, I can no longer send a test email or campaigns from Acymailing.
Both during the Spam test and when sending an email test, a rotating arrow remains visible and nothing else happens. No error message appears either.
A test from Joomla with the Global configuration works fine.
So the PHP Mail function continues to work well.
Could it be something at the provider on the server that is preventing mail from Acymailing from being sent?
Or can I fix it somewhere in Acymailing itself?