Suddenly Amazon SES stopped working


Hi to everyone, suddenly a lot of email i'm sending with SES raise an exception saying receive this message: "SMTP server requires a secure connection or the client is not authenticated. The server response was: Authentication required"

I didn't change anything, this happened on its own out of nowhere ( we send I found this: but i found out that my user has been created in 2020 ( so after the mentioned date ). I've also tried to create a new "Access Key" for the same user but it gives me the same error.

The strange thing is that not every mail gets this error.. some of them are sent as usual. We send about 800k/900k mails per month with SES and never had an issue.

Can someone give me som help?

thank you very much to everyone

2 Answers

Hi, the error message that you get form SMTP server happens usually with improper SSL authentication from client. So, do you send your 800k mails from one or multiple mail clients? Do they all authenticate the exact ame way if you use multiple?

To debug, you may want to try via CLI using

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answered a year ago
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reviewed a year ago
  • Hi, thanks for your answer. The mail are sent by the same client ( it is a .net Application that sends notification mails ), so the authentication is the same. Another strange thing is that not all the mails fail. About 20% fails, the others simply works as before.. i can't understand why some connection get accepted and some don't. The connections are made from the same ip / device / client. Even debugging the application give no more clue, the problem seems to be in the authentication but no more info are given. Now i'll try to use the CLI to see if i can get more info.


Just for info, i tried with the CLI and i got the exact same problem, so the problem seems not to be with the client used.

answered a year ago

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