What is the best email frequency for high volume transactional emailing?

Let's say we send about 100k emails per day to our users. These are all transactional emails ("You received a new message",etc.)

In or开发者_C百科der to reduce the number of emails we group those transactions into summary emails and send those summary emails every 6 hours or so. So every 6 hours or so we send about 25k emails.

From particularly hotmail's perspective is it a bad practice to send all these emails every six hours.

Would it be better to send these emails every hour for instance?

Thanks, Haluk

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The best way to send - is to send uniformly. Every hour is better then every 6 hours. Every minute is better. Think how mail services like gmail work. They send and receive mail every minute. If you'll send a large chank of mail at a short time and then will do a delay - that will look more like spam.