> ## Documentation Index > Fetch the complete documentation index at: https://ahasend.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Batch Processing > Send high-volume emails efficiently with the CLI # Batch Processing Send high-volume personalized emails efficiently using the AhaSend CLI batch processing capabilities. ## Overview Batch processing allows you to: * Send thousands of personalized emails * Use concurrent workers for speed * Track progress in real-time * Automatically retry failures * Generate performance metrics ## Recipient File Formats Create `recipients.csv`: ```csv theme={null} email,name,first_name,company,account_type john@example.com,John Doe,John,ACME Corp,premium jane@example.com,Jane Smith,Jane,Tech Inc,basic alice@example.com,Alice Johnson,Alice,StartUp Ltd,enterprise ``` Create `recipients.json`: ```json theme={null} [ { "email": "john@example.com", "name": "John Doe", "substitution_data": { "first_name": "John", "company": "ACME Corp", "account_type": "premium" } } ] ``` ## Basic Batch Send ```bash theme={null} ahasend messages send \ --from noreply@example.com \ --recipients recipients.csv \ --subject "Welcome to {{company}}" \ --html-template welcome.html \ --progress \ --show-metrics ``` ## Performance Options ### Concurrency Control ```bash theme={null} # Conservative (1 worker) ahasend messages send \ --recipients users.csv \ --html-template template.html \ --max-concurrency 1 # High performance (5 workers - default) ahasend messages send \ --recipients users.csv \ --html-template template.html \ --max-concurrency 5 # Maximum throughput (10 workers) ahasend messages send \ --recipients users.csv \ --html-template template.html \ --max-concurrency 10 ``` ### Performance Comparison | Concurrency | Emails/Hour | Use Case | | ----------- | ----------- | --------------------- | | 1 | \~3,600 | Testing, low priority | | 5 | \~18,000 | Standard campaigns | | 10 | \~36,000 | Maximum throughput | ### Progress Tracking ```bash theme={null} ahasend messages send \ --recipients large-list.csv \ --html-template newsletter.html \ --max-concurrency 5 \ --progress ``` ## Error Handling ### Automatic Retries ```bash theme={null} ahasend messages send \ --recipients users.csv \ --html-template template.html \ --max-retries 3 ``` ### Failed Recipients Recovery Failed recipients are automatically saved for retry: ```bash theme={null} # If failures occur, retry with saved file ahasend messages send \ --recipients ~/.ahasend/failed-2024-01-16-143022.json \ --html-template campaign.html \ --max-retries 5 ``` ## Template Personalization ### Global and Per-Recipient Data ```json theme={null} // global-data.json { "company_name": "ACME Corp", "support_email": "support@acme.com" } ``` ```bash theme={null} ahasend messages send \ --from noreply@acme.com \ --recipients users.csv \ --subject "{{first_name}}, Welcome to {{company_name}}" \ --html-template welcome.html \ --global-substitutions global-data.json ``` ## Best Practices ### 1. Test with Small Batches First ```bash theme={null} # Test with first 10 recipients head -11 recipients.csv > test-batch.csv ahasend messages send \ --from sender@example.com \ --recipients test-batch.csv \ --html-template template.html \ --sandbox ``` ### 2. Use Idempotency Keys ```bash theme={null} ahasend messages send \ --recipients users.csv \ --html-template template.html \ --idempotency-key "campaign-$(date +%Y%m%d)" ``` ### 3. Monitor Performance ```bash theme={null} # Send with detailed logging ahasend messages send \ --recipients users.csv \ --html-template template.html \ --verbose \ --show-metrics \ --output json ``` ## Troubleshooting **Slow Performance**: Increase `--max-concurrency` up to 10 workers **High Failure Rate**: Verify domains and check suppressions list **Memory Issues**: Process large files in smaller chunks ## Next Steps * [Learn about templates](/cli/templates) * [Set up webhook monitoring](/cli/webhook-testing)