last 6 months monthly charge is under $1, this month it's over $100. However my mailer activity is down, having reduced my mailing list (email address IDs) from 5000 to 1200.

The significant increase in your monthly charge from under $1 to over $100, despite reducing your mailing list, is unusual and warrants investigation. Given that your mailer activity has decreased, we would typically expect your costs to decrease as well.

There are a few potential explanations for this unexpected cost increase:

1. Dedicated IP: You may have switched to using a dedicated IP address for sending emails. Dedicated IPs have a fixed monthly cost, starting at $24.95 per month for a standard dedicated IP or $15 per month plus usage fees for a managed dedicated IP. This could explain a sudden increase in your monthly charges.

2. Additional Services: You might have enabled additional Amazon SES features or related AWS services that come with their own costs, such as Virtual Deliverability Manager or increased usage of other AWS services like EC2, S3, or CloudWatch in conjunction with your email sending.

3. Billing Cycle Change: There could have been a change in how your usage is being billed or a delay in billing from previous months that is now being reconciled.

4. Unexpected Usage Spike: Although you've reduced your mailing list, there might have been an unexpected spike in email sending activity, perhaps due to a misconfiguration or an automated process.

To understand the reason for this increase, I recommend the following steps:

1. Check your AWS Cost Explorer to see a detailed breakdown of your charges.
2. Review any recent changes to your SES configuration, especially regarding IP addresses or additional features.
3. Verify that there hasn't been any unauthorized use of your account.
4. Contact AWS Support for a detailed explanation of the charges if you can't identify the cause through your own investigation.

Remember, Amazon SES typically charges based on the number of emails sent and received, as well as for any additional features you're using. The reduction in your mailing list size alone doesn't necessarily correlate directly to cost if other factors have changed.
Sources
Amazon Simple Email Service Pricing | Cloud Email Service | Amazon Web Services
the monthly expenses I'm paying | AWS re:Post

Hello Peter,

Since this issue pertains to charges, I recommend reaching out to the AWS Support team. They will be best equipped to identify what went wrong or determine if any resources were launched on your end that may have triggered this cost.

Thank you. Best regards,