TimeToInbox
Optimize Your Email Deliverability with Time to Inbox Metrics
Measure, monitor, and improve how quickly your emails reach recipient inboxes
Gain insights into email delivery performance and ensure your messages arrive promptly
What is Time to Inbox (TTI)?
Time to Inbox (TTI) is a critical email deliverability metric that measures the time it takes for an email to travel from the sender's server to the recipient's inbox. This metric provides valuable insights into email delivery performance and can help identify potential deliverability issues.
According to Postmark, a leading email service provider, "Time to Inbox is the length of time it takes from when an email is sent from a client until it is logged as delivered." [1]
Unlike other email metrics that focus on recipient engagement (opens, clicks), TTI focuses on the technical aspects of email delivery, helping you understand if your emails are being delivered promptly or experiencing delays in the delivery pipeline.
Why TTI Matters
In today's fast-paced digital environment, the timing of email delivery can significantly impact the effectiveness of your email communications:
- Time-sensitive communications like password resets, verification codes, and urgent notifications need to arrive quickly
- Marketing campaigns timed for specific events lose effectiveness if delayed
- Transactional emails such as order confirmations and receipts should arrive promptly to reduce customer anxiety
- System notifications for critical events need immediate delivery to enable timely responses
Benefits of Monitoring Time to Inbox
Improved Deliverability
Identify and resolve delivery bottlenecks to ensure emails reach inboxes faster and more reliably.
Enhanced User Experience
Provide a better experience for recipients by ensuring time-sensitive communications arrive promptly.
Increased Engagement
Improve open and click-through rates by delivering emails when recipients are most likely to engage.
Provider Comparison
Compare email service providers based on actual delivery performance to make informed decisions.
Early Issue Detection
Detect delivery problems before they impact your communication strategy or business operations.
Performance Optimization
Fine-tune your email infrastructure and sending practices based on concrete delivery metrics.
Key Email Deliverability Metrics
While Time to Inbox (TTI) is a crucial metric for measuring email delivery performance, it's part of a broader set of deliverability metrics that provide a comprehensive view of your email program's health:
Time to Inbox (TTI)
The time it takes for an email to travel from the sender's server to the recipient's inbox, measured in seconds or milliseconds.
Inbox Placement Rate
The percentage of emails that successfully reach recipients' inboxes rather than spam folders or being blocked entirely.
Delivery Rate
The percentage of emails that were successfully delivered to recipients' mail servers (not necessarily inboxes).
Bounce Rate
The percentage of emails that were rejected by recipient mail servers, including both hard and soft bounces.
Spam Complaint Rate
The percentage of delivered emails that recipients mark as spam, a critical factor affecting sender reputation.
Open Rate
The percentage of delivered emails that recipients open, providing insight into subject line effectiveness and inbox placement.
Forward Email's Time to Inbox Performance
Forward Email is committed to transparency in email deliverability, providing real-time Time to Inbox (TTI) metrics that demonstrate their exceptional delivery performance. As the only email service with 100% open-source and transparent monitoring, Forward Email sets the standard for deliverability transparency. [2]
Industry-Leading Delivery Times
Forward Email continuously monitors how long it takes for emails sent through their service to be delivered to test inboxes at major email service providers. Their engineering team is automatically alerted if any delivery times exceed 10 seconds, ensuring consistent performance.
Current Time to Inbox metrics for Forward Email based on their monitoring data:
Email Service Provider TTI Comparison
Data sources: Forward Email Monitoring, Postmark TTI Monitoring, and Mailtrap Research. See citations below for details.
Did you know? Forward Email is the only email service with 100% open-source and transparent monitoring. Source code is available on GitHub.
Forward Email's TTI Monitoring Code
forwardemail/forwardemail.net// TTI monitoring implementation from Forward Email's codebase
const ms = require('ms');
const Axe = require('axe');
const dayjs = require('dayjs');
const imap = require('imap');
class TTIMonitor {
constructor(options = {}) {
this.options = options;
this.axe = new Axe({
logger: options.logger
});
this.alertThreshold = ms('10s');
}
async measureTTI(provider, mode = 'direct') {
const startTime = Date.now();
const testId = generateUniqueId();
// Send test email with unique ID
await this.sendTestEmail(testId, provider, mode);
// Poll inbox until email is found or timeout
const deliveryTime = await this.pollInbox(testId, provider);
// Calculate TTI
const tti = deliveryTime - startTime;
// Alert if TTI exceeds threshold
if (tti > this.alertThreshold) {
await this.sendAlert(provider, mode, tti);
}
return {
provider,
mode,
tti,
timestamp: dayjs().format()
};
}
}Email Service Provider TTI Comparison
When choosing an email service provider, Time to Inbox performance is a critical factor that directly impacts the effectiveness of your communications. Below is a comparison of average TTI metrics across popular email service providers based on published data:
| Email Service Provider | Average TTI | Data Source |
|---|---|---|
| Forward Email | 1.6s - 1.7s | Forward Email Monitoring [2] |
| Postmark | 11.96s - 23.23s | Postmark TTI Monitoring [1] |
| SendGrid | Inbox placement: 61.0% | Mailtrap Research [3] |
| Mailgun | Inbox placement: 71.4% | Mailtrap Research [3] |
| Amazon SES | Inbox placement: 77.1% | Mailtrap Research [3] |
Note: TTI measurements can vary based on testing methodology, recipient email providers, and network conditions. The data above represents published metrics from each provider's own monitoring or independent research.
Factors Affecting Time to Inbox
Sender Reputation
Your sender reputation significantly impacts how quickly emails are processed. Email service providers prioritize delivery from senders with established positive reputations.
According to Mailtrap research, email service providers only account for about 30% of your email deliverability, with sender practices making up the rest. [3]
Infrastructure Quality
The quality and configuration of your email infrastructure, including servers, IP addresses, and authentication protocols (SPF, DKIM, DMARC), directly affect delivery speed.
Email Volume
Sending large volumes of email simultaneously can trigger rate limiting or throttling by recipient servers, increasing delivery time.
Content Quality
Emails with spam-like content, excessive images, or poor HTML structure may undergo additional filtering, delaying inbox placement.
Recipient Provider
Different email providers implement varying levels of filtering and processing. Gmail, Outlook, Yahoo, and others each have unique delivery characteristics.
Authentication Status
Properly authenticated emails with valid SPF, DKIM, and DMARC records typically experience faster delivery times than unauthenticated messages.
Implementing TTI Monitoring
Set Up Seed Addresses
Create test email accounts across major providers (Gmail, Outlook, Yahoo, etc.) to serve as monitoring endpoints.
Implement Tracking
Add unique identifiers to test emails and implement server-side logging to record send and delivery timestamps.
Establish Baselines
Collect initial data to establish baseline TTI metrics for different recipient providers and message types.
Set Up Alerts
Configure alerting thresholds to notify your team when TTI exceeds acceptable limits.
Regular Testing
Schedule regular test sends to continuously monitor TTI performance and detect trends or issues.
Forward Email handles TTI monitoring automatically for all customers, with transparent reporting and proactive alerts if delivery times exceed thresholds.
Learn More About Forward EmailTTI Optimization Use Cases
Password Reset Emails
Users waiting for password reset links expect near-instant delivery. Optimizing TTI ensures users can quickly regain access to their accounts without frustration.
Time-Sensitive Notifications
Alerts about security incidents, system outages, or critical updates need to reach recipients promptly to enable timely action.
Transactional Confirmations
Order confirmations, shipping notifications, and payment receipts should arrive quickly to reduce customer anxiety and support inquiries.
Two-Factor Authentication
Authentication codes sent via email must arrive within seconds to provide a seamless login experience without disrupting the user's workflow.
Event Reminders
Reminders for upcoming events or appointments should arrive with sufficient lead time to allow recipients to prepare or reschedule if necessary.
System Monitoring Alerts
IT teams rely on prompt delivery of system alerts to address issues before they impact users or business operations.
Ready to Optimize Your Email Delivery?
Forward Email provides industry-leading Time to Inbox performance with transparent monitoring and reporting. Experience the difference that fast, reliable email delivery can make for your business.
Citations & References
- Postmark. (2025). Time to Inbox. Retrieved April 6, 2025, from https://tti.postmarkapp.com/
- Forward Email. (2025). Time to Inbox. Retrieved April 6, 2025, from Forward Email's Time to Inbox monitoring page.
- Bostogannashvili, K., Kaitaz, D., & Hurchenko, Y. (2025, January 6). Email Deliverability Comparison Results [2025]. Mailtrap. Retrieved April 6, 2025, from https://mailtrap.io/blog/email-deliverability-comparison/