Not sure if this is related to all those SMTP reports, but I have encountered a problem with my (non-AWS) S3 series when uploading:
SSL_connect returned=1 errno=0 peeraddr=13.75.95.95:443 state=error: certificate verify failed (unable to get local issuer certificate)
I checked the certificate and it seems fine as I have been able to connect to the S3 bucket.