A very important note for all that use SMTP as mailing option instead of PHP.
You will run into erros when using the newsletter mailing:
PHP Question2Answer email send error: SMTP Error: The following recipients failed: firstname.lastname@example.org: Limit of 250 e-mails per hour exceeded, please try again in 60min. or contact your support.
Hundreds of such errors in my error log file...
I guess the only fix is to contact the hosting provider!
Or changing the settings of your server.