---
title: "Time to Inbox (TTI) - Real-time email delivery speed monitoring"
description: "See how fast Lettermint delivers transactional emails. Real-time Time to Inbox measurements track speed from API call to inbox arrival across all major providers."
url: "https://lettermint.co/time-to-inbox-tti"
---


# Time to Inbox (TTI)

Time to Inbox (TTI) measures the complete journey of an email, from the moment it is sent through the Lettermint API until it arrives in the recipient's inbox. It is a real-world speed test that shows how long customers actually wait to receive their password resets, order confirmations, and other critical emails.

Lettermint publishes live TTI metrics for the major email providers so anyone can verify delivery speed, not just take our word for it. When it comes to transactional email, every second counts.

## How Time to Inbox is measured

Lettermint sends test emails every 10 minutes, around the clock, to the major providers using the exact same API and infrastructure that customers use. The test emails receive no special treatment, so the numbers reflect real performance. The measurement follows these stages:

1. **Send.** A test email is sent through the standard Lettermint API, the same path every customer email takes. The stopwatch starts here.
2. **Process.** Lettermint's transactional infrastructure processes and routes the message just like any other email. Test emails are never prioritized, which keeps the measurement fair.
3. **Deliver.** The message is handed off to the recipient's email provider.
4. **Provider validation.** The receiving provider runs its own spam, authentication, and security checks before accepting the message. This step is outside Lettermint's control, but everything is optimized to pass it quickly.
5. **Inbox arrival.** The email lands in the inbox and is ready to open. The timer stops here.
6. **Calculate TTI.** The difference between the send time and the inbox arrival time is the Time to Inbox.

## Why Time to Inbox is stricter than "delivery time"

Most delivery-speed figures published by email services measure a much shorter journey. Their stopwatch starts when the message leaves their backend and stops when the receiving mail server accepts it during the SMTP handshake. That is stage 3 above. It says nothing about what happens next: the recipient's provider still has to run its spam, authentication, and security checks and place the message in the inbox, and that is often where the real waiting happens.

Lettermint's Time to Inbox covers the whole flow, from the API call to the moment the email is visible in the inbox. It includes queueing, processing, handoff, provider validation, and inbox placement. Because the number is measured end to end, it is a stricter benchmark than server acceptance time and the only one that reflects what a recipient experiences. A one-second acceptance time is not useful if the message then sits in a provider's scanning queue for a minute.

Even measured this way, transactional emails sent through Lettermint typically reach the inbox within a few seconds. When comparing delivery speed between email services, compare end-to-end inbox arrival times, not the time until a mail server accepts the message.

## Typical Time to Inbox

Time to Inbox is measured in seconds, not minutes. Across the monitored providers, most test emails reach the inbox within roughly 5 to 10 seconds, and the fastest arrive in under a second. Some providers occasionally take longer during busy periods. The live, per-provider figures are published on this page and refreshed every 10 minutes, so the numbers reflect current performance rather than a marketing claim.

## Current Time to Inbox per provider

| Provider | Latest | 24-hour average | 24-hour median | 24-hour 90th percentile |
| --- | --- | --- | --- | --- |
| Gmail | 9.31 s | 4.56 s | 4.28 s | 6.83 s |
| Yahoo | 4.15 s | 4.99 s | 4.88 s | 7.19 s |
| Outlook | 7.59 s | 8.28 s | 7.25 s | 10.54 s |
| iCloud | 8.00 s | 9.49 s | 8.89 s | 12.54 s |
| Proton Mail | 4.82 s | 6.20 s | 5.15 s | 10.95 s |
| AOL | 5.40 s | 5.01 s | 4.73 s | 7.14 s |
| GMX | 4.95 s | 4.23 s | 4.11 s | 6.15 s |
| Zoho | 6.56 s | 4.47 s | 4.32 s | 6.56 s |

Snapshot taken 2026-10-22 18:00 UTC. Values are seconds from API call to inbox arrival, measured end to end every 10 minutes. Live figures: https://lettermint.co/time-to-inbox-tti (JSON: https://api.lettermint.co/rest/v1/tti/measurements).

## Which email providers are monitored

Lettermint continuously monitors Time to Inbox for Gmail, Yahoo, Outlook, iCloud, Proton Mail, AOL, GMX, and Zoho. Together these represent the vast majority of email addresses worldwide, giving a comprehensive view of delivery performance across different systems.

## What Time to Inbox means for transactional vs broadcast email

Transactional emails, such as password resets, order confirmations, and receipts, are triggered by a user action and are expected instantly. Broadcast emails, such as newsletters and campaigns, are sent to many recipients at once and are less time-sensitive.

Lettermint keeps these two types completely separated. When someone requests a password reset, it cannot get stuck behind thousands of newsletters in a queue. Critical messages get their own fast lane, which is what keeps transactional Time to Inbox low.

## Dedicated infrastructure and separate IP pools

Lettermint maintains dedicated servers and separate IP pools for [transactional email](https://lettermint.co/features/transactional-emails) and [broadcast email](https://lettermint.co/features/broadcast-emails). Newsletter campaigns do not slow down password resets, and marketing sends do not affect transactional sender reputation. This separation is a core reason transactional emails arrive quickly and consistently.

## What affects email delivery speed

Several factors influence how fast an email reaches the inbox:

- Provider processing and queue times
- Spam filtering and content scanning
- Authentication checks (SPF, DKIM, DMARC)
- Network conditions between sender and provider
- The content and reputation of the sending domain

Lettermint optimizes everything within its control, but each provider runs its own validation processes that every email must pass through.

## Why fast Time to Inbox matters

Users expect transactional emails instantly. When someone resets a password or completes a purchase, waiting even a few minutes creates doubt about whether the action worked. Fast, consistent delivery builds trust and keeps users moving forward without interruption.

## How to improve your Time to Inbox

To keep delivery speed high, maintain a good sender reputation, set up correct authentication (SPF, DKIM, DMARC), keep email content clean and relevant, and send through reliable infrastructure like Lettermint. Avoiding spam triggers and keeping consistent sending patterns also helps.

## How to monitor your own Time to Inbox

Lettermint provides analytics for delivery, opens, and bounces so you can track how your own emails perform over time. Watching these metrics alongside the public Time to Inbox page helps you spot changes early and confirm that your transactional flow is landing in the inbox.

## Monitoring, alerting, and what happens when Time to Inbox is high

Lettermint tracks Time to Inbox 24/7. When elevated values are detected, the team investigates immediately. High values usually point to provider-side delays or broader network issues. Lettermint works with providers and adjusts routing to restore normal speeds as quickly as possible. Publishing these metrics publicly keeps Lettermint accountable for maintaining fast delivery for everyone.

## Frequently asked questions

### What is Time to Inbox (TTI)?
Time to Inbox measures the complete journey of an email from the moment it is sent through the Lettermint API until it arrives in the recipient's inbox. It shows how long customers actually wait for their password resets, order confirmations, and other critical emails.

### How is Time to Inbox measured?
Lettermint sends test emails every 10 minutes to major providers using its standard API and infrastructure. Once sent, the email is retrieved from the inbox and its headers are checked for the exact arrival time. The difference between sending and arrival is the Time to Inbox.

### How is Time to Inbox different from delivery time?
Delivery time usually means the time until the receiving mail server accepts a message, which excludes the provider's spam and security checks and inbox placement. Time to Inbox measures the full flow from API call to visible inbox arrival, so it is a stricter number and the one that matches what recipients actually experience. Lettermint publishes this end-to-end figure, and it is typically a few seconds.

### Which email providers are monitored?
Lettermint continuously monitors Gmail, Yahoo, Outlook, iCloud, Proton Mail, AOL, GMX, and Zoho.

### Are test emails prioritized for better results?
No. Test emails go through the exact same infrastructure as customer emails and receive no special treatment. This ensures the measurements reflect the real performance customers experience.

### How can I improve my Time to Inbox?
Maintain a good sender reputation, ensure proper authentication (SPF, DKIM, DMARC), keep content clean and relevant, and use a reliable [transactional email provider](https://lettermint.co/features/transactional-emails) like Lettermint. Avoid spam triggers and keep consistent sending patterns for the best results.

### Why do transactional emails need a fast Time to Inbox?
Users expect transactional emails instantly. Waiting even a few minutes for a password reset or purchase confirmation creates frustration. Fast delivery builds trust and keeps users moving forward.

### What happens when Time to Inbox is high?
When elevated Time to Inbox values are detected, the Lettermint team investigates immediately. High values usually indicate provider-side delays or broader network issues. Lettermint works with providers and adjusts routing to restore normal speeds as fast as possible.