SmtpClient fail to send email using Amazon SES endpoint

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I'm using .Net SmtpClient to send emails with Amazon SES.

The emails can't be sent from some PCs and I get a timeout.

I read the Amazon doc -> https://repost.aws/knowledge-center/smtp-connectivity-timeout-issues-ses

I'm investigating if this could be a TLS issue, because the command they ask to run doesn't complete (which is probably causing the SmtpClient timeout issue as well)

openssl s_client -crlf -starttls smtp -connect email-smtp.us-east-1.amazonaws.com:587

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[EDIT]

I've run a Wireshark trace on a Working PC

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And then on a non-working PC

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I'm not sure what it means... Any thoughts?

Thanks!

  • Side note, the emails works on most devices in my inventory but does not work on 2 specific computers.

1 回答
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Hello.

What about doing a packet capture using something like "tcpdump"?
Regarding the "tcpdump" command, this answer may be helpful.
https://repost.aws/questions/QUlQYKoGVNQkuKY_bdyU5DNg/ses-update-tls-connections-to-1-2-to-maintain-aws-connectivity#ANuiqMgNVxTLqHA90aDR7SWw

I don't think it's very likely, but could it be blocked by the OS's firewall?

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已回答 5 个月前
  • Using Wireshark, I see there is a difference in the network trace between a working/non-working environment. See my Edits with screen capture in my original post.

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