Time to Inbox (TTI)

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

We send test emails every 10 minutes to major providers using our standard API and infrastructure. Once sent, we retrieve the email from the inbox and check its headers to see the exact arrival time. The difference between sending and arrival gives us the Time to Inbox.

Delivery time usually means the time until the receiving mail server accepts a message. It leaves out 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. For Lettermint it is typically a few seconds.

We continuously monitor Gmail, Yahoo, Outlook, iCloud, Proton Mail, AOL, GMX, Zoho. These represent the vast majority of email addresses worldwide, giving you a comprehensive view of delivery performance across different systems.

Several factors impact speed: provider processing times, spam filtering, authentication checks, network conditions, and email content. While we optimize everything on our end, each provider has their own validation processes that emails must pass through.

No, our test emails go through the exact same infrastructure as your emails. We don't - and can't - give them special treatment. This ensures our measurements reflect the real performance you and your customers experience.

Maintain good sender reputation, ensure proper authentication (SPF, DKIM, DMARC), keep your content clean and relevant, and use a reliable transactional email provider like Lettermint. Avoid spam triggers and maintain consistent sending patterns for best results.

Users expect transactional emails instantly. When someone resets their password or completes a purchase, waiting even a few minutes creates anxiety and frustration. Fast delivery builds trust and keeps your users moving forward without interruption.

When we detect elevated Time to Inbox values, our team investigates immediately. High values usually indicate provider-side delays or broader network issues. We work with providers and adjust our routing to restore normal speeds as quickly as possible.