AWS SES OTP mail to Gmail got delayed by 4 minutes

Question

The DKIM, SPF, DMARC all passed.

There was a 4 minutes delay between Date and Received header here. 2 mail got delayed to the same gmail address. Another email that was sent 10 minutes later was received by only 1 second delayed to the same address.

What might be the delaying cause here and how can I improve OTP mail delay?

Received-SPF: pass (google.com: domain of [REDUCTED]@us-west-1.amazonses.com designates 23.251.242.7 as permitted sender) client-ip=23.251.242.7;
From: Our Service <noreply[REDUCTED]>
To: [REDUCTED]
Subject: Our Service Registration Verification
Message-ID: <[REDUCTED]@us-west-1.amazonses.com>
Content-Transfer-Encoding: 7bit
Date: Tue, 25 Feb 2025 08:44:21 +0000
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Feedback-ID: ::1.us-west-1.YPwg6VteZskXBbEPTmgY5Ucp7bb3jWAKHKJr2nWtx0c=:AmazonSES

Your verification code is: 123456

re:Post Agent · Accepted Answer

The 4-minute delay you experienced in email delivery from AWS SES to Gmail could be attributed to several factors:

1. Greylisting: This is a common anti-spam technique used by email providers like Gmail. When an unknown sender tries to deliver an email, the receiving server temporarily rejects it. The sending server (in this case, Amazon SES) then retries after a delay. This process can cause delays of a few minutes to several hours.

2. Email queuing: Amazon SES, like other email services, may queue emails before sending them, especially during high-traffic periods or when dealing with rate limits imposed by receiving email providers.

3. Network latency: Although less likely to cause a 4-minute delay, network issues between Amazon SES and Gmail's servers could contribute to slower delivery times.

4. Eventual consistency: Amazon SES uses a distributed computing model called eventual consistency. This means that changes or actions in the system take some time to propagate across all servers, which could potentially affect email sending times.

To improve OTP mail delivery times:

1. Implement IP warming: Gradually increase your sending volume to establish a good reputation with email providers.

2. Use dedicated IP addresses: This can help you maintain a consistent sending reputation and potentially reduce the likelihood of greylisting.

3. Monitor your sending statistics: Keep an eye on bounce rates, complaint rates, and other metrics that could affect your sender reputation.

4. Optimize email content: Ensure your emails don't contain elements that might trigger spam filters.

5. Consider using alternative channels for time-sensitive OTPs: SMS or push notifications might be more suitable for immediate delivery of one-time passwords.

6. Set up SNS notifications: This will help you monitor bounces, complaints, and delivery statuses more closely.

7. If the issue persists, contact AWS Support for further investigation and assistance.

Remember that occasional delays can happen due to various factors, some of which are beyond your control. The fact that a subsequent email was delivered with only a 1-second delay suggests that the issue may not be persistent or systemic.  
**Sources**  
[Amazon SES emails slow to receive | AWS re:Post](https://repost.aws/questions/QUdl6NhnWeRfyq0i9-oZKbow/amazon-ses-emails-slow-to-receive)  
[Troubleshoot greylisting in Amazon SES | AWS re:Post](https://repost.aws/knowledge-center/ses-troubleshoot-greylisting)  
[Amazon SES Delivery problems - Amazon Simple Email Service](https://docs.aws.amazon.com/ses/latest/DeveloperGuide/troubleshoot-delivery.html)

AWS SES OTP mail to Gmail got delayed by 4 minutes

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