Amazon Simple Email Service is ending support for Signature Version 3

we didnt

We didn't get any such notification. Are you sending emails via SMTP or API?
If you are using the API it might be related to the SDK version that you are using. Try updating that.

Hi @looloo,

I'm not sure if you got sorted but if not allow me to share my insight in-case anybody else faces this issue going forward :

Your DKIM is not affected as the deprecation notification of AWS Signatre V3 below is more related to the AWS Signature used when access AWS SES APIs.

Beginning October 1st, 2020, Amazon SES will only support requests signed using Signature Version 4. If you use an older version of the AWS Signature, you must adopt AWS Signature Version 4 prior to that date. 

How to migrate to the AWS Signature Version 4

1. AWS SDK/CLI :

If you use an AWS SDK or the AWS CLI, you should update to the most recent version of the SDK or the AWS CLI.

2. AWS SES SMTP :

AWS SES SMTP credentials are signed, and previous to February 2019 AWS used SignatureV2 when generating credentials via the SES console. You will need to generate new set of SMTP credentials using AWS SES console which will be pre-signed using the AWS V4 signature.

3. AWS API :

If you make direct HTTPS requests to the Amazon SES API, update the headers in your requests to use AWS Signature Version 4 such as Algorithm=AWS4-HMAC-SHA256

You can find an example of a call to the Amazon SES API that uses the AWS Signature V4 in Amazon SES API requests.

Should you have any follow-up questions related to this reported issue feel free to let us know by clicking the comment button.