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I am a Cox Gigablast user in Phoenix, AZ. Since Wednesday, May 20, 2020, I am no longer able to send email from Mozilla Thunderbird using a third party email (email@example.com). This has been working for many years and I didn't make any software changes recently. I also have all the latest versions and patches of Windows and Thunderbird installed.The error I am getting in a popup after I send the email is
An error occurred while sending mail. The mail server responded: <firstname.lastname@example.org> sender rejected. Refer to Error Codes section at www.cox.com/.../email-error-codes.html for more information. AUP#CXSNDR. Please check the message and try again.
I am using the following SMTP config: smtp.cox.net port 465 Normal Password SSL/TLS