What is AWS Region? How to choose it?

You need to select the region that best suits you and your subscribers’ location for SES Region. And remember to choose this exact same region when you apply to Amazon for a sending limit increase.
If your AWS account is already out of the Sandbox (in a specific AWS region), use that region for MailBluster.
For example, We have our sending limit increased for the region “Oregon”. In MailBluster, we will select “Oregon” as region when setting up AWS credentials.

In your Amazon account,

AWS account details and sending limits

In MailBluster,

MailBluster brand ses region settings