Email Throttling

Email throttling is the practice of deliberately controlling the rate at which emails are sent to prevent overwhelming receiving servers, avoid triggering spam filters, and maintain good sender reputation. This technique involves spacing out email delivery over time rather than sending large volumes simultaneously. For cold email marketers, throttling is essential for maintaining deliverability and preventing ISPs from classifying bulk sending as potential spam activity.

ISPs implement their own throttling mechanisms to protect their infrastructure and users from email flooding. When senders attempt to deliver too many emails too quickly to a single ISP, that provider may temporarily defer or reject additional messages until sending rates decrease. Different ISPs have varying tolerance levels – Gmail might accept hundreds of messages per hour from established senders while smaller providers might limit acceptance to dozens per hour. Exceeding these limits can trigger temporary blocks or longer-term reputation damage.

Implementing effective email throttling requires understanding recipient distribution and ISP-specific limits. Spread your cold email campaigns over several hours or days rather than sending everything at once. Many email service providers offer built-in throttling controls that automatically manage sending rates. For large campaigns, consider segmenting your list by ISP and implementing different throttling rates for each provider. Start with conservative sending rates for new domains or IP addresses, gradually increasing volume as you establish positive sending history. Monitor bounce rates and delivery delays that might indicate throttling by receiving servers. Remember that throttling is particularly important for cold email because recipients haven’t explicitly requested your messages, making ISPs more sensitive to volume spikes from your domain.