What’s the difference between native SMTP and third-party relay?

The sending infrastructure choice affects how your email appears to recipients and mailbox providers.

Native SMTP:

• Connects directly to your mailbox provider (Gmail, Outlook, Google Workspace)
• Messages appear to come from your actual email account
• Uses the provider's sending infrastructure
• Subject to provider's sending limits and policies
• Standard approach for cold email tools

Third-party relay:

• Routes email through a sending service (SendGrid, Mailgun, Amazon SES)
• Uses the relay's IP infrastructure
• Higher volume capabilities
• Typically prohibited for cold email by relay terms of service

Why cold email uses native SMTP:

• Messages appear as individual sends, not bulk
• Leverages personal mailbox reputation
• Enables true threading and reply detection
• Mimics human sending behavior

Tradeoffs:

• Native SMTP has lower volume limits
• Relay offers better deliverability infrastructure (for legitimate use)
• Cold email requirements don't fit relay terms of service
• Native approach is appropriate for outreach use case