Configuring CiviCRM for 1and1 email limits
At Administer > CiviMail > Mailer Settings (civicrm/admin/mail) you can configure how many mail go out in each mail run. Limit the batch to 100 per run.

Combining your cron schedule with Administer > Settings > Scheduled Jobs (civicrm/admin/job), you can control the Run Frequency for task  Send Scheduled Mailings. The options for the this are "every time" or "hourly" (or larger intervals), so you probably want to set "every time" here, and then configure the cron task to be called every three minutes or more.

Scheduled jobs in CiviCRM (documentation) are triggered by an external task, for 1and1 customers via SSH to the hosting account. This is where you'll most likely dictate the frequency at which your scheduled jobs may be run.

With all that done, your CiviMail should stay under the limits ... unless additional emails are generated as well. What happens if you hit that limit - say if your CRM is partway through a mailout - and a donor's receipt or password reset email gets trashed for being email number 101 or 102? It might not be likely, but only your org can decide if it's acceptable, and you'll never know for sure how much buffer to allow.

So, the above configuration can mostly avoid hitting 1and1's limits. But ... please see my other answer :)