Hi, i am trying to send email from a web site which was upgraded from 2003 to 2005.
I am having problem to send email to other email add.

smtp: mail.company.com

i can send and receive email on any@company.com, but for email other than anyemail@company.com, such as gmail, yahoo etc....it will give the below errors

Bad sequence of commands. The server response was: This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Net.Mail.SmtpException: Bad sequence of commands. The server response was: This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.

Thanks in advance

its because you send the email through an smtp server

if you are on your own network, most likely you can get authenticated, or it might have a relay address to where you can send to, no security issues

when you try to send from a remote server, it will require authentication and only if they do allow you to send through them

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