Problem: No mail content to send

Hello everyone!

Before writing these lines, I have searched the Forum but have not found a solution yet, so I hope someone can help me:

I installed and configured J!MailAlerts as described in the Manual:

- Set up alert, frequency 5 minutes
- set up the cron (every 5 minutes, working)
- Allow Users Select Plugins: No
- Respect Last Email Date: yes
- Is Default Alert For New User: yes
- Allowed frequencies / default frequency: 5 Minutes
- Enable batch: yes
- Batch size: 400
- synced some test users to the alert

but have the following problem:

although the list of user subscriptions shows the correct time of last sync by cronjob, for example 18:10, J!MailAlerts does not recognize new articles and therefore sends no mail, writing

"No new mail content to send" into the log file.

What am I doing wrong?

Thank you very much in advance for your help.

Kind regards,
Michael