If you are implementing AWS SES to send e-mails via the API and you get the error SignatureDoesNotMatch, then it's very possible that you are using the SMTP credentials. The SMTP credentials only works when sending via SMTP, so in order to send via the API, you need to creare a new IAM User and manually attach the permissions needed, like this one:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"ses:SendRawEmail"