I'm the regular user for AWS SES, and I got the quota for 50K per days, and 28 mail per seconds, I usually send transactional mail, about 1000 per day. It works fine. But, I want to send some bulk promotion mail to my clients this time. It show "SMTP Error: Could not authenticate" frequently after I send about 1000~ mails. But, some of them are still sent correctly. I got "SMTP Error: Could not authenticate" for about 30%~50% email sending. I use phpMailer and send mail in a for loop and it takes about 3 seconds for sending one mail. It seems I'm not over the quota or something I need to take care?
Is this an error you are getting today? I had similar issues earlier today on much lower volumnes and according to the aws status page, they had some issues today: