You may use the built-in Nexternal Mail Wizard to send a bulk email, or export the list to Mailchimp for sending.
First, segment the customers who will receive the email:
1. Orders / Advanced Search / Order Search: Date Range=? (click search)
2. Orders / Advanced Search / Line Item Search: Product=? (click finish)
Note that the line item search in Step #2 will search only the results of the order search in Step #1.
Then send the email:
3. Customers / Mail Wizard: Contact Criteria=Search Results (Order Search, Line Item Search) Click Next, and continue with the Mail Wizard to send your email.
If you have integrated your Order Management System (OMS) with a Mailchimp account and would prefer to export this list to Mailchimp for emailing instead of using the OMS built-in Mail Wizard, then the alternative Step #3 is Customers /Export (to a pre-created Mailchimp list [now called an audience]). Then send your email from there.