Summary
One-time password (OTP) emails are expected to arrive almost instantly, with user experience significantly impacted by delays beyond 5-10 seconds. While the ideal is near-instantaneous delivery, various external factors-such as recipient server load, network conditions, and spam filtering-can cause variability, sometimes extending delivery times to several minutes for specific services. Senders have limited direct control over the final time an email appears in an inbox beyond optimizing their sender reputation and leveraging their Email Service Provider's efficiency. Therefore, accurate measurement relies not on universal benchmarks, which are often impractical, but on comprehensive internal tracking. This involves comparing the timestamp of email initiation to its successful receipt, utilizing ESP logs, webhooks, and specialized monitoring tools. Regularly assessing overall email program health, including bounce rates and delivery to specific mailbox providers, further helps in optimizing and ensuring timely OTP delivery.
Key findings
- High User Expectation for Speed: Users generally expect OTP emails to arrive almost instantly, ideally within 5-10 seconds. Delays beyond 15-30 seconds can significantly degrade user experience and potentially lead to frustration or security concerns if the OTP expires.
- Variability in Real-World Delivery: While transactional emails are optimized for speed, actual delivery times can vary. Factors like recipient server throttling, spam filters, server load, network conditions, and even specific service policies can introduce delays, sometimes extending to several minutes for certain providers.
- Limited Sender Control Over Latency: Senders have limited influence over the final time an email appears in the inbox beyond their Email Service Provider's queuing efficiency and their own sender reputation. External factors, particularly on the recipient's end, play a significant role.
- Latency is Crucial for OTPs: Latency, the time it takes for an email to be sent and received, is a critical metric for time-sensitive OTP emails. Low latency, ideally under a few seconds, is essential to ensure a smooth and secure user authentication process.
- Benchmarks Are Highly Specific: Universal, hard benchmarks for email delivery time are often unmeasurable or unreliable due to the multitude of external factors involved. Program health is better assessed through consistent delivery rates and internal measurement.
Key considerations
- Focus on Internal Measurement: Rather than seeking hard, universal delivery benchmarks, focus on measuring the time from email send initiation to OTP entry or confirmed inbox receipt within your own system, as this is more actionable and relevant.
- Utilize ESP Tools and Logs: Leverage your Email Service Provider's activity feeds, event webhooks, API responses, and detailed logs. These resources provide precise timestamps for send, processing, and delivery events, allowing for accurate latency calculation.
- Implement End-to-End Monitoring: Employ a combination of detailed system logs, CloudWatch metrics, dedicated email testing tools, or even a controlled test mailbox to track the complete journey from application initiation to actual inbox arrival, providing a comprehensive view of delivery performance.
- Monitor Program Health: Regularly assess overall email program health by monitoring bounce rates. Consistently high delivery rates, typically 98% or more without major bounce issues, indicate a generally well-performing program, even for time-sensitive OTPs.
- Break Down Delays by Provider: Analyze delivery time distributions and identify delays specific to certain mailbox providers. This granular insight can help pinpoint bottlenecks and inform strategies for improving deliverability to those specific domains.
What email marketers say
10 marketer opinions
For one-time password emails, user expectations lean heavily towards rapid delivery, ideally within seconds to ensure a seamless authentication process. While the goal is near-instant arrival, real-world delivery times can fluctuate due to factors beyond a sender's immediate control, such as recipient server loads, network conditions, or spam filtering. Consequently, precise measurement is crucial and should center on tracking the latency from the moment an OTP email is initiated by an application to its actual receipt by the user. This involves leveraging detailed logs from Email Service Providers, utilizing webhooks for delivery events, and implementing dedicated monitoring solutions, rather than seeking universal, often elusive, delivery benchmarks. Continuously monitoring overall email program health, including consistent delivery rates and low bounce rates, further supports effective OTP delivery.
Key opinions
- User Expectation: Seconds: Users anticipate OTP emails to arrive almost instantly, often within 5-10 seconds, with anything beyond 15-20 seconds typically leading to frustration and a degraded experience.
- Measurement Focus: End-to-End: Effective measurement of OTP delivery time focuses on the entire journey, from the application's initiation of the email to its successful arrival in the recipient's inbox, rather than relying on broad, unmeasurable benchmarks.
- Influencing Factors and Limitations: While senders optimize for speed, recipient server behavior, throttling, and spam filters are significant external factors that can introduce delays, limiting a sender's direct control over final inbox placement time.
- Logs and Timestamps are Key: Measuring involves comparing the timestamp of email initiation with timestamps from ESP logs, webhooks, or the moment the user reports receipt, providing concrete data points for latency analysis.
- Crucial for User Experience & Security: Rapid OTP delivery is not just a convenience; it's vital for a smooth user authentication flow and to prevent security issues arising from expired codes due to delays.
Key considerations
- Prioritize Internal Latency Tracking: Implement robust internal systems to track the time elapsed from when your application initiates an OTP email to when it's confirmed delivered to the recipient's mail server or inbox.
- Utilize ESP Delivery Events: Leverage your Email Service Provider's webhooks, API responses, and detailed activity logs, which provide precise timestamps for delivery events, crucial for calculating accurate latency.
- Assess Overall Email Health: Regularly review your email program's overall health indicators, such as bounce rates and consistent delivery rates (e.g., 98%+), as these indirectly reflect the efficiency of your OTP delivery system.
- Monitor Specific Mailbox Provider Performance: Analyze delivery time distributions for different mailbox providers to identify and address any specific bottlenecks or consistent delays with particular domains.
- Beyond Raw Delivery Time: Consider the time from email send to OTP entry by the user, as this reflects the full user experience and can reveal issues beyond just email delivery.
Marketer view
Marketer from Email Geeks explains that email is not instant messaging and many factors influence delivery time, making benchmarks highly specific. He suggests assessing program health by looking at bounce rates, noting that high bounce rates often indicate deferred delivery. If delivery rates are consistently 98%+ without major bounce issues, the program is likely performing well. He also mentions seed list services as a potential, albeit flawed, source for delivery time data.
27 May 2024 - Email Geeks
Marketer view
Marketer from Email Geeks advises measuring the time from email send to OTP entry rather than looking for hard time-to-deliver benchmarks, which are often unmeasurable. He suggests breaking down delays by mailbox provider and analyzing distribution. He also notes that tracking pixel image load timestamps can be useful for measurement. Additionally, he explains that senders have limited influence over time-to-inbox beyond ESP queuing and reputation deferrals, and users generally expect some delay with OTP emails.
10 Dec 2022 - Email Geeks
What the experts say
3 expert opinions
The goal for one-time password (OTP) emails is near-instant delivery, ideally within a few seconds, given their time-sensitive nature for user authentication. However, real-world delivery can sometimes extend to several minutes, as noted by some experts observing services like major banks. This latency, defined as the time from email initiation to receipt in the inbox, is influenced by various factors. These include the sender's IP reputation, proper authentication (SPF, DKIM, DMARC), recipient server load, network issues, and even greylisting. To accurately measure OTP delivery performance, it's essential to track the end-to-end journey by recording timestamps from the moment an email is sent to its confirmed arrival, often through automated testing tools and dedicated monitoring systems.
Key opinions
- OTP Delivery Expectations: While OTP emails are ideally expected to arrive within a few seconds, real-world delivery can sometimes take several minutes, as observed with services from major financial institutions.
- Understanding Email Latency: Email delivery latency encompasses the total time from when a sender's server completes sending a message to its acceptance by the recipient's server, and then its appearance in the inbox.
- Low Latency is Essential: Achieving low latency, ideally under a few seconds, is critical for OTP emails to ensure a smooth user experience and prevent security issues from expired codes.
- Factors Influencing Delays: Various factors can introduce delays, including server load, network issues, recipient server processing, IP reputation, sender authentication (SPF, DKIM, DMARC), and greylisting.
Key considerations
- Measure End-to-End Latency: Measure OTP delivery latency by tracking timestamps from the moment an email is sent by your system to its confirmed arrival in the recipient's inbox.
- Leverage Automated Monitoring: Utilize automated tools and dedicated monitoring systems that send test messages and record the precise end-to-end delivery time for consistent tracking.
- Optimize Sender Factors: Ensure strong IP reputation and correct implementation of sender policies like SPF, DKIM, and DMARC, as these significantly impact delivery speed and inbox placement.
Expert view
Expert from Email Geeks shares his personal experience with OTP emails, noting that delivery times for banks like Chase and services like Atlassian can often be several minutes.
5 Mar 2024 - Email Geeks
Expert view
Expert from Spam Resource explains that latency in email delivery is the time it takes for an email to be sent and received. He states that while many email systems prioritize speed, delays can occur due to server load, network issues, or receiving server processing. He suggests measuring latency by sending emails to a known set of test addresses and recording the time from send initiation to receipt, using automated tools for consistent tracking. For time-sensitive emails like OTPs, low latency is critical.
12 May 2025 - Spam Resource
What the documentation says
5 technical articles
Major Email Service Providers (ESPs) like Twilio, SendGrid, Postmark, AWS SES, and Microsoft 365 services universally optimize for low latency in transactional emails such as one-time passwords (OTPs), often delivering within seconds. While no specific delivery time Service Level Agreements (SLAs) are typically provided due to external variables, these providers emphasize their systems are designed for speed and high throughput. Measuring actual OTP delivery times relies heavily on the robust logging and event notification features offered by each ESP, allowing senders to track the journey from their system's send initiation to the recipient's mail server acceptance.
Key findings
- ESPs Optimize for Speed: Leading Email Service Providers are engineered for rapid delivery of transactional emails like OTPs, aiming for delivery within seconds.
- No Specific SLAs: Providers generally do not offer explicit Service Level Agreements (SLAs) for OTP email delivery times, acknowledging the inherent variability caused by external network conditions and recipient server behavior.
- Provider-Specific Measurement Tools: Each Email Service Provider offers dedicated tools for measuring delivery, including API responses and service logs, activity feeds and Event Webhooks, detailed activity logs and webhooks, CloudWatch metrics and Event Destinations, and Message Trace.
- Focus on Internal Timestamps: Accurate measurement primarily involves tracking timestamps provided by the Email Service Providers, from the point of message dispatch from their system to its acceptance by the recipient's mail server.
Key considerations
- Leverage ESP-Specific Monitoring: Utilize the unique monitoring and logging features provided by your chosen Email Service Provider, such as API responses, activity feeds, webhooks, or dedicated dashboards, to accurately track OTP email delivery performance.
- Track Send-to-Delivery Timestamps: Focus on measuring the time elapsed between your system initiating the email send and the Email Service Provider's confirmation of delivery to the recipient's mail server, using the timestamps provided in their logs or event notifications.
- Acknowledge External Variables: Understand that factors outside of your Email Service Provider's control, such as recipient mail server processing, network conditions, and spam filtering, can introduce variability and impact the final delivery time to the inbox.
- Utilize Event Notifications: Configure webhooks or event destinations from your Email Service Provider to receive real-time updates and detailed timestamps for delivery events, enabling precise latency analysis for your OTP emails.
Technical article
Documentation from Twilio Docs explains that while Twilio Verify does not provide a specific SLA for OTP email delivery time due to external factors like network conditions and client behavior, the service is designed for speed. Measurement can be inferred from API responses and service logs, indicating when the message was sent from their end.
5 Jun 2024 - Twilio Docs
Technical article
Documentation from SendGrid Docs states that while there isn't a specific OTP email delivery SLA, their transactional email service is optimized for low latency. Measurement can be achieved by utilizing their activity feed or Event Webhooks, which provide detailed timestamps and delivery statuses for tracking how quickly emails are processed and delivered.
23 Aug 2024 - SendGrid Docs
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