Some emails from .Net getting a 530 Authentication Required error

I have a form in my app built in ASP.Net that allows users to send email to any email address. The "From" name and email address are by default set to the signed-in user's name and email.

When I send out an email using the same form, they go just fine. But whenother users try it their email gets bounced back and they get the following error in the bounced email:




"Could not deliver message to the following recipient(s):


Failed Recipient: [emailaddressofrecipient]


Reason: Remote host said: 530 Authentication required"


Any ideas on why it would work for me and not for others? My email is of the domain that DASP hosts while others are not. I am using localhost as the smtp host.


Here' my code that I use for the email form:


Dim objEmail As New MailMessage


Dim emailFrom As New MailAddress(FromAddress.Value, FromName.Value)


Dim smtp As New SmtpClient


objEmail.From = emailFrom


objEmail.Sender = emailFrom


objEmail.ReplyTo = emailFrom


'Collect recipient emails from the To ListBox


For Each item As ListItem In lstEmailTo.Items


objEmail.To.Add(New MailAddress(item.Value, item.Text))


Next





objEmail.IsBodyHtml = True


objEmail.Priority = drpPriority.SelectedValue


objEmail.Subject = strSubject


objEmail.Body = strBody


smtp.Host = "localhost"


smtp.Send(objEmail)


objEmail = Nothing





Thanks in advance for your help,


Jimmy

 

The remote email is fine as they receive and send emails from it all day long. It's only when theysend through my app via DASP (I'm using localhost as the SMTP host)when they get that email bounced back to them with that error.

Any other ideas?

 

I think the problem is at their end. They have an comprehensive spam-blocking mechanism and have asked us for smtp IP address so they can whitelist the server from which the users' emails are being generated. Since we use localhost in the app, I don't have much information to provide to them so I'vecreateda support ticket.


I'm working with them to see if we can find a solution. Willpost when found.


Thanks,


Jimmy