However, sending email via SES currently uses an older piece of external code which uses the older (v3) signature method.
AWS is retiring v3 signatures on October 1 2020, so this pathway will stop working.
Update the pathway to use PhutilAWSFuture, which provides v4 signatures.
T13235 discusses poor error messages from SES. Switching to Futures fixes this for free, as they have more useful error handling.