File sharing problme

[John]

Hi

I am emailing a file as attachment using the code;

Dim MailMsg As New MailMessage(New MailAddress(strFrom.Trim()), New
MailAddress(strTo))
MailMsg.Attachments.Add(New System.Net.Mail.Attachment("MyFile.txt"))

Dim SmtpMail As New SmtpClient
....
SmtpMail.Send(MailMsg)

SmtpMail = Nothing
MailMsg = Nothing

Then I try to append to the same file using;
IO.File.AppendAllText(("MyFile.txt", "Some text") and I get the below error;

System.IO.IOException was unhandled
Message="The process cannot access the file 'MyFile.txt' because it is
being used by another process."
Source="mscorlib"

How can I close the link of the file from email system so it is available
for append without problem?

Thanks

Regards