SES sender address blocked by Microsoft smtp server

For a couple of weeks I have intermittently had emails bouncing from hotmail, yahoo, etc. with reports like:

`An error occurred while trying to deliver the mail to the following recipients: xxxx@hotmail.co.uk

Reporting-MTA: dns; b232-1.smtp-out.ap-southeast-2.amazonses.com

Action: failed Final-Recipient: rfc822; xxxx@hotmail.co.uk Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [69.169.232.1] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [DB8EUR05FT037.eop-eur05.prod.protection.outlook.com] Status: 5.7.1`

As far I I can see, it is the result of Microsoft blocking one or more Amazon SES server addresses. What is the correct way to get Amazon SES to investigate and correct this issue?