You can use the SELECT INTO statement to export formatted data to a file.

Data Export with an SQL Query

The following query exports data into a file formatted in comma-separated values (CSV):

SELECT Id, MessageBody INTO [csv://Inbox.txt] FROM [Inbox] WHERE From = 'test@test.com'

You can specify other formats in the file URI. The possible delimiters are tab, semicolon, and comma with the default being a comma. The following example exports tab-separated values:

SELECT Id, MessageBody INTO [csv://Inbox.txt;delimiter=tab] FROM [Inbox] WHERE From = 'test@test.com'

C#

String connectionString = "user=myuseraccount;password=mypassword;";

using (GmailConnection connection = new GmailConnection(connectionString)) {
  GmailCommand cmd = new GmailCommand("SELECT Id, MessageBody INTO [csv://Inbox.txt] FROM [Inbox] WHERE From = 'test@test.com' ", connection);
  int rowsAffected = cmd.ExecuteNonQuery();
} 

VB.NET

Dim connectionString As [String] = "user=myuseraccount;password=mypassword;" 

Using connection As New GmailConnection(connectionString)
  Dim cmd As New GmailCommand("SELECT Id, MessageBody INTO [csv://Inbox.txt] FROM [Inbox] WHERE From = 'test@test.com'", connection)
  Dim rowsAffected As Integer = cmd.ExecuteNonQuery()
End Using

You can specify other file formats in the URI. The following example exports tab-separated values:

C#

String connectionString = "user=myuseraccount;password=mypassword;";

using (GmailConnection connection = new GmailConnection(connectionString)) {
  GmailCommand cmd = new GmailCommand("SELECT * INTO [Inbox] IN [csv://filename=c:/Inbox.csv;delimiter=tab] FROM [Inbox] WHERE From = 'test@test.com'", connection);
  int rowsAffected = cmd.ExecuteNonQuery();
} 

VB.NET

Dim connectionString As [String] = "user=myuseraccount;password=mypassword;" 

Using connection As New GmailConnection(connectionString)
  Dim cmd As New GmailCommand("SELECT * INTO [Inbox] IN [csv://filename=c:/Inbox.csv;delimiter=tab] FROM [Inbox] WHERE From = 'test@test.com'", connection)
  Dim rowsAffected As Integer = cmd.ExecuteNonQuery()
End Using