SmtpClient fail to send email using Amazon SES endpoint

Question

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

I've run a Wireshark trace on a Working PC

And then on a non-working PC

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

Thanks!