Definition
Send pacing is the deliberate management of the rate at which emails are dispatched during a campaign. Rather than sending all emails as quickly as the infrastructure allows, pacing spreads delivery over a defined period — minutes or hours — to maintain a consistent sending volume that receiving servers are more likely to accept.
Sudden volume spikes are one of the most common triggers for delivery throttling. A sender that normally dispatches 10,000 emails per hour but suddenly sends 500,000 in the same window will raise alarms at recipient servers. Pacing smooths the flow and makes the sender's behaviour appear stable and predictable.
How Pacing Works
Most email platforms and SMTP services allow configuration of hourly or per-minute send rate limits. The platform divides the total campaign size by the desired delivery window and throttles dispatch accordingly. For example, 100,000 emails sent over two hours would dispatch approximately 833 per minute.
Best Practices
- Maintain consistent pacing patterns across campaigns — erratic pacing is almost as harmful as volume spikes
- Set pacing limits below provider thresholds to avoid triggering automatic rate limiting
- Monitor delivery log data during the send to confirm pacing is working as configured
- Adjust pacing during IP warm-up periods, starting slow and gradually increasing over weeks
Related Glossary Terms
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Classification
Bounce classification uses SMTP codes (550, 551, 552, 553, 554, 450, 451, 452) and enhanced status codes to categorise permanent and transient delivery failures.
Email Deliverability
Email deliverability is the ability to land in the recipient's inbox rather than the spam folder. It depends on sender reputation, authentication, list quality, and content practices.
DMARC Alignment
DMARC identifier alignment determines whether the domain in the From header matches the domains used in SPF and DKIM authentication. Strict or relaxed.
Acceptance Rate
Acceptance rate is the percentage of emails submitted for delivery that are accepted by the recipient's mail server, representing the first deliverability checkpoint before inbox placement is determined.
Email Acceptance Rate
Email acceptance rate measures the percentage of emails accepted by recipient mail servers versus total sent. It is a core deliverability metric that reveals whether your sending infrastructure is trusted by receiving servers.