We help IT Professionals succeed at work.

SMTPClient error: "Command parameter not implemented. The server response was: <serverhostname>: Helo command rejected: need fully-qualified hostname"

salted
salted asked
on
Medium Priority
5,547 Views
Last Modified: 2008-01-09
I'm getting this exception from the SmtpClient class: "Command parameter not implemented. The server response was: <(serverhostname)>: Helo command rejected: need fully-qualified hostname"

        SmtpClient sc = new SmtpClient();
        sc.Host = "mail.******.com";
        sc.Send(mm);

How can I make smtpclient send the FQDN instead of the hostname?
Comment
Watch Question

Éric MoreauSenior .Net Consultant
CERTIFIED EXPERT
Top Expert 2016

Commented:
Hi salted,

see if you can find something in this FAQ: http://www.systemnetmail.com/

Cheers!
This is probably security on the smtp server you are using.
When an SMTP session starts it is generally initiated with the following command sent by the sender:

    HELO hostname

where hostname is the name of the sending host.

Some smtp servers will do a reverse dns lookup of the hostname and compare the ip address against the IP address of the sending host.
This is basically to stop spammers and spoofers.

As a result they will not accept mail from hosts that do not have an FQDN (fully qualified domina name) or from hosts they cannot lookup using reverse DNS.
Sprry, I didn't read the last line of your post.
I guess you know the above.
I'm afraid its a bug/feature of the SmtpClient.
Microsoft are aware : http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=94378

Not the solution you were looking for? Getting a personalized solution is easy.

Ask the Experts

Author

Commented:
Thanks guys,

I decided to set credentials and login to the smtp server over ssl - bypassing the need for a FQDN.

Seems MS could do with adding support for this.

Thanks for all your help!
Access more of Experts Exchange with a free account
Thanks for using Experts Exchange.

Create a free account to continue.

Limited access with a free account allows you to:

  • View three pieces of content (articles, solutions, posts, and videos)
  • Ask the experts questions (counted toward content limit)
  • Customize your dashboard and profile

*This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

OR

Please enter a first name

Please enter a last name

8+ characters (letters, numbers, and a symbol)

By clicking, you agree to the Terms of Use and Privacy Policy.