Returns a list of completed sends (campaigns) within a given date range, including per-campaign statistics and content.

Filtering

• Date range is inclusive: start_date from 00:00:00, end_date until 23:59:59
• Optional campaign_folder_name filters by the letter folder name. If no matching folder is found, an empty result set is returned
• Only sends with status DONE are included

Notes

• The content field in each campaign item contains the plain-text version of the letter (HTML stripped). If no plain-text version exists, it falls back to stripped HTML
• Statistics are retrieved from cache when available for performance