Since Bookem doesn't do email campaigns (only bulk SMS campaigns), you can export your client list to send bulk emails in external bulk emailing apps such as MailChimp or SendGrid. The format of the file that is exported is a comma separated value (.CSV) file. This format is widely accepted by bulk email platforms.
You also usually won't need to worry about importing duplicate clients, such as when you download and upload the same clients multiple times, since external platforms such as MailChimp automatically de-duplicate imported contacts.
Follow these steps:
To export all clients: Go to Clients > click on 'Export Clients' at the top of the page and follow the prompt
To export clients with past bookings only: Go to your Calendar and click on the top right kebab menu icon and click 'Download'
When prompted, select Spreadsheet (CSV), enter a date range and click 'Download'
Use this CSV file to import into mailing apps for bulk email sending. Instructions vary by platform.