Possible to split mail batches?

I'm hoping someone can point me in the right direction in this matter.

I have set up two sets of rules:

1. On publication of an article, an e-mail notification will be sent to all authenticated users.
2. Everytime a comment is added to an article, rules fetches all users that flagged the node and sends all "Followers" an update by e-mail.

Both rules work fine in the testing evironment with about 10 users. Instantly.
In practice the website will have 100 - 300 registered users.

I have been in contact with the webhoster and they have asked me to seperate these mail batches. Preferably into set of 50, seperated by 30 minutes.

Is there a way to achieve this with Rules?
Should I be looking into another (sub)module?