known issue Amazon SES: 451 4.4.2 Timeout waiting for data from client

[Sonya*]

I send email through Amazon SES via SMTP settings in IPS. All my emails (about 1,200 a day) are delivered without issues. But sometimes (3 to 4 times a day), I see these errors in email error logs:

All the topics listed here have 70 followers or more. I have never seen this error on topics with quite a few followers. What can be a reason for this error?

• IPS issue?
• Server issue with SMTP?
• Amazon SES issue?

I have consulted @stoo2000 and he has been looking into this over the last few days. His theory is: Invision Community holds connections to the SMTP server open throughout the whole time of the execution of background tasks. So it might be sending an email in the first loop and then not send another email for a while, performing other background tasks. Then it tries to send another email and fails due to timeout. This is just a theory. He hasn't seen this come up before. 

Note: I do not have any other errors with emails. They are all delivered. About 99% of registrations are confirmed. My bounce rate is very healthy. This is the only issue I have and only on topics with large number of followers. 

Does someone have an idea, what the reason for the error can be?

Edited March 5 by Sonya*

[Jim M]

Are you only noticing this on topic follow notifications? Just wanted to understand if this is randomly showing up on other items, that may point more towards a server issue.

[Sonya*]

Just now, Jim M said:

Are you only noticing this on topic follow notifications?

Yes. Only topic notifications. No other random errors.

[Jim M]

Thanks! I have opened a bug report for this internally for our developers to test further and investigate.