Definition
Email send velocity is the speed at which a sender injects email into the sending infrastructure, normally measured in messages per hour (or per second). It is distinct from total volume: two senders can have equal volume but very different velocities depending on how quickly they push the queue.
Most ESPs and sending platforms throttle velocity — capping how many messages go out per hour and per second — to protect sender reputation and comply with receiving-side expectations.
How Throttling Affects Velocity
| Setting | What It Controls |
|---|---|
| Messages per hour cap | Maximum throughput over an hour |
| Bulk vs normal tier | Higher-volume senders get higher caps |
| Connection limits | Simultaneous SMTP connections increase velocity |
| Per-recipient rate | Rate limiting to individual domains |
Bumping against a throttle is normal for large sends; the queue drains at the capped rate rather than all at once.
Why Velocity Matters
- Sudden spikes look suspicious: A sharp burst of mail from a previously quiet domain can trigger scrutiny.
- Recipient domain rate limits: Mailbox providers have limits for how much mail a domain accepts quickly.
- Reputation protection: Gradual, consistent sending is easier on sender reputation than erratic bursts.
- Delivery timing: Velocity determines how long a large campaign takes to fully reach the inbox.
How to Manage Send Velocity
- Stagger large sends: Spread a high-volume campaign over hours or days rather than one burst.
- Use connection and job throttling: Configure your ESP's throughput settings to a sustainable level.
- Warm up before scaling: Gradually increase velocity on new IPs and domains.
- Monitor feedback: Watch for complaints or delivery dips when raising velocity.
Related Glossary Terms
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An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
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AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
Email Authentication Protocols
Email authentication protocols are technical standards that verify the identity of an email sender, helping mailbox providers distinguish legitimate mail from spam and phishing.
BIMI
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Bounce Management
Bounce management is the process of handling emails that are rejected by mailbox providers, including classification, removal of bad addresses and protection of sender reputation.
Frequently Asked Questions
Email send velocity is the rate at which a sender injects email into its sending infrastructure, usually measured in messages per hour or per second. It controls how quickly a campaign reaches recipients' inboxes.
Throttling is a deliberate limit on how fast you can send, set by your ESP or platform to protect deliverability. High volumes beyond the cap are queued and sent at the allowed rate, which is normal for large campaigns.
Yes. Abrupt, erratic bursts of mail can appear suspicious and trigger scrutiny, while gradual, consistent sending is easier on sender reputation. Matching your velocity to your volume and history supports healthy delivery.
Increase your platform's throttle limits, add or optimise SMTP connections, and — for a new IP or domain — warm up by gradually raising volume and velocity over time before attempting high-throughput sends.