Some emails are delayed

Question

We have been using AWS SES for at least  7 years and lately there is some strange delay on emails which makes it unusable. We use it for emailing stuff from our application. The application is used by about 30 customers, and each customer uses a different identity (email-from-address).

At first I thought it had to do with a certain identity, since only one customer complained. And some quick tests suggested that this was the case, but now that I've scratched my head for about 24 hours I did some further testing on other customers and saw that they also seems to have issues. Only that they haven't reported anything yet.

We are using SES through the API, and on our side we use Perl. But that should not be an issue since we get the confirmation string/GUID from the API, which we also logs.

**What I've noticed while testing**

Sent 10 emails within about 10 minutes.
* Firstly they did not come in order. 
* Some emails was delivered almost instant.
* Most of the emails were delivered within 10 minutes.
* The last email came 6.5 hours after sending it.

Any ideas?

Best Regards, 
Joakim

Sumit Bhardwaj · Answer

SES is a relay agent which takes the email from your API then filter it as per standards and accept it if all good. Then it setup connection with recipient MTA and handover the email to recipient MTA. Once SES got SMTP 250 OK from recipient MTA we donot have any visibility how recipient MTA process the email.

There could be below mentioned possible reason behind delay:

1) If recipient MTA is not able to accept new connections then SES will keep retrying. If you want notification for each retry then you can configure the same by referring
https://aws.amazon.com/about-aws/whats-new/2020/06/amazon-ses-can-now-send-notifications-when-the-delivery-of-an-email-is-delayed/

2) Recipient MTA accepts the email and then keeps that in buffer before landing it in recipients inbox.

3) Recipient MTA facing some throttling hence not processing the emails at given time.

4) Rare but possible if recipient MTA has SES IP addresses in filtering hence you may facing throttle issues.

In order to resolve this please open support case with AWS and share below mentioned:

1) From email address, To email address, Time stamp and Message ID from logs if possible.

By having this information SES team will analyze the internal logs in order to find root cause and that's how they will help you to resolve this issue.

Some emails are delayed

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