The nice and slow CRM?

I have a collection of around 250 high quality lead emails. I expect around a 40% reply rate and a 10% booking sale. I don't want to blow that load of emails at one shot and completely overwhelm my business and frustrate my contacts. Can anyone suggest a slow email automation where I can send 5 emails each day? Preferably working in Gmail/Workspace and free to use if possible.

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Thank you!