Auto email from IP is bouncing back

I'm working on an e-commerce website based on ASP Vb. which has auto email(HTML) after people placing order, requesting forgotten password, etc.
MY problem is after email has sent, basically I get bounce back almost from most email careers but gmail. Is there any way to prevent this issue?
Here is my email configuration:

webmaster.Configuration.Fields.Item _
("http://schemas.microsoft.com/cdo/configuration/sendusing")=2

webmaster.Configuration.Fields.Item _
("http://schemas.microsoft.com/cdo/configuration/smtpserver")= My IP Address

webmaster.Configuration.Fields.Item _
("http://schemas.microsoft.com/cdo/configuration/smtpserverport")=25 
webmaster.Configuration.Fields.Update

Examples:

comcast.net: This is an automatically generated Delivery Status Notification. Unable to deliver message to the following recipients, due to being unable to connect successfully to the destination mail server. emailaddress@comcast.net Final-Recipient: rfc822;emailaddress@comcast.net Action: failed

Another one: This is an automatically generated Delivery Status Notification. THIS IS A WARNING MESSAGE ONLY. YOU DO NOT NEED TO RESEND YOUR MESSAGE. Delivery to the following recipients has been delayed. emailaddress@satx.rr.com Final-Recipient: rfc822;emailaddress@satx.rr.com

Thanks in advance for your time and opinion!

Answer

Many automated systems don't bother to follow the RFCs and just send email out the Internet. As a result the look more like spammers than legitimate e-mailers. As a result they have problems getting their mail delivered, or get their mail classified as Spam. Either send the mail to your own mail server for delivery, or setup your server with an RFC compliant mail server. It may be easier to relay mail via your own mail server.

Review my rules for Detecting Email Server Forgery. It starts out listing the characteristics of a legitimate server. Try to configure your setup to meet all of them. At the end of the document is a list of Verification Services as well as a list of Documentation Resources.