Q: What's the difference between SMTP and REST API?
- REST API: Simple HTTP POST endpoint (
/api/send) for sending emails with JSON payload - recommended for modern applications - SMTP: Standard email protocol, works with all email libraries and clients - better for legacy systems or when using existing SMTP libraries
Both methods support campaign tracking for broadcast traffic. When sending bulk/marketing emails via SMTP, declare X-Stream-Type: broadcast to receive automatic campaign-level bounce monitoring and reputation protection.
Q: What SMTP ports do you support?
- Port 587 (STARTTLS - recommended)
- Port 2525 (alternative STARTTLS)
- Port 25 is not supported
- Port 465 (SSL) may be added in the future
Q: Can I send attachments?
Yes, attachments are fully supported via SMTP. Maximum email size including attachments is 10MB.
Q: How many recipients can I send to per email?
Maximum 50 recipients per email. For larger lists, send multiple emails or use our bulk sending features.
Q: What's the sending rate limit?
Rate limits are configurable per customer and depend on your IP type:
- Shared IPs: Default 50 emails/second (3,000/minute, 180,000/hour)
- Dedicated IPs: Default 500 emails/second (30,000/minute, 1.8M/hour)
- Batch Sending: Up to 1,000 recipients per API call
These are starting defaults. Higher limits available for high-volume senders with good reputation. Contact support to increase your throughput.
Q: Why are my emails going to spam?
Common causes:
- Domain not verified (ensure SPF, DKIM, DMARC configured)
- Poor content (use content scoring API)
- Low engagement rates
- High bounce/complaint rates
- New IP needs warm-up