• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 4224
  • Last Modified:

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

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";

How can I make smtpclient send the FQDN instead of the hostname?
  • 2
1 Solution
Éric MoreauSenior .Net ConsultantCommented:
Hi salted,

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

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
saltedAuthor 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!
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

  • 2
Tackle projects and never again get stuck behind a technical roadblock.
Join Now