How to send customer a copy of web order form

With increasing frequency I am receiving email delivery failure notices related to emails sent from my business web site. When a customer places an order, an email facsimile of the order is sent to me and a copy is sent to the customer. During the last year or so I’ve noticed an increase in emails that were undeliverable. The notices cited reason 550 which was defined sometimes as being on a blocked list and sometimes as “unknown host.”

To send a copy of the order form to our customer I use a few lines of visual basic, as follows:

        Dim MM As New MailMessage()
        MM.From = New MailAddress("")
        'next line takes email address entered
        'by customer on the order form and adds to CC
        MM.Body = "---------------------------------"
        'Body of email created here
        MM.Priority = MailPriority.Normal

My little company sends very few advertising emails and only to existing customers. However, bounced order-copy emails that totaled about one per month a year ago now are almost one a day. I was wondering if I could send the order form copy email using a different  coding technique which would reduce the likelihood of being mistakenly considered spam? Or is this sending technique violating some sort of spam detection algorithm?
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Ricky MartireIT Design ArchitectCommented:

Usually the cause of the spam filters detecting that your script that is sending emails isn't coming from the SMTP server authoritive for your domain i.e. using sendmail directly from the web server at your hosting company.  

A good 'quick' way to solve this is to get it to send through the SMTP server that all of your domains outgoing mails come from.  You may, of course need to change the script to make it authenticate with the SMTP server depending on how that is set up.

If the above isn't helpful, if you post some more about the set up of the web server i.e. whether its inside your network or at a web hosting company etc then I may be able to help further.
efzAuthor Commented:
I think you're saying that it's not ideal to use a "From" address that isn't the real address of the SMTP server that is sending the mail, right?

Is it possible to simply change the "MM.From" line?
Ricky MartireIT Design ArchitectCommented:
That's correct, changing the from to something the SMTP attached to that we servers send mail would solve it

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