Excel – Exporting emails from an Outlook subfolder to Excel

You can use a library called ExcelLibrary. It's a free, open source library posted on Google Code:

ExcelLibrary

This looks to be a port of the PHP ExcelWriter that you mentioned above. It will not write to the new .xlsx format yet, but they are working on adding that functionality in.

It's very simple, small and easy to use. Plus it has a DataSetHelper that lets you use DataSets and DataTables to easily work with Excel data.

ExcelLibrary seems to still only work for the older Excel format (.xls files), but may be adding support in the future for newer 2007/2010 formats.

You can also use EPPlus, which works only for Excel 2007/2010 format files (.xlsx files). There's also NPOI which works with both.

There are a few known bugs with each library as noted in the comments. In all, EPPlus seems to be the best choice as time goes on. It seems to be more actively updated and documented as well.

Also, as noted by @АртёмЦарионов below, EPPlus has support for Pivot Tables and ExcelLibrary may have some support (Pivot table issue in ExcelLibrary)

Here are a couple links for quick reference:
ExcelLibrary - GNU Lesser GPL
EPPlus - GNU (LGPL) - No longer maintained
EPPlus 5 - Polyform Noncommercial - Starting May 2020
NPOI - Apache License

Here some example code for ExcelLibrary:

Here is an example taking data from a database and creating a workbook from it. Note that the ExcelLibrary code is the single line at the bottom:

//Create the data set and table
DataSet ds = new DataSet("New_DataSet");
DataTable dt = new DataTable("New_DataTable");

//Set the locale for each
ds.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;
dt.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;

//Open a DB connection (in this example with OleDB)
OleDbConnection con = new OleDbConnection(dbConnectionString);
con.Open();

//Create a query and fill the data table with the data from the DB
string sql = "SELECT Whatever FROM MyDBTable;";
OleDbCommand cmd = new OleDbCommand(sql, con);
OleDbDataAdapter adptr = new OleDbDataAdapter();

adptr.SelectCommand = cmd;
adptr.Fill(dt);
con.Close();

//Add the table to the data set
ds.Tables.Add(dt);

//Here's the easy part. Create the Excel worksheet from the data set
ExcelLibrary.DataSetHelper.CreateWorkbook("MyExcelFile.xls", ds);

Creating the Excel file is as easy as that. You can also manually create Excel files, but the above functionality is what really impressed me.

This is an old question, but here is a solution that works for me, modifying code from a few sources. You can modify it to your requirement.

This allows the user to select any folder, either under the default locations or even in another archive or PST file. If the user selects Cancel in the folder picker, then the email is saved to the default sent mail folder.

Private Sub Application_ItemSend(ByVal Item As Object, _
                                 Cancel As Boolean)
    Dim objNS As NameSpace
    Dim objFolder As MAPIFolder
    On Error Resume Next
    Set objNS = Application.Session
    If Item.Class = olMail Then
        Set objFolder = objNS.PickFolder

        'save to a folder under the default structure, main PST/archive
        If Not objFolder Is Nothing And IsInDefaultStore(objFolder) And objFolder.DefaultItemType = olMailItem Then
            Set Item.SaveSentMessageFolder = objFolder

        'save to a non-default, different PST/archive
        ElseIf Not IsInDefaultStore(objFolder) Then
            Set objFolder = GetFolderFromPath(objFolder.FolderPath)
            Set Item.SaveSentMessageFolder = objFolder

        'neither, just save to default sent items folder
        Else
            Set objFolder = objNS.GetDefaultFolder(olFolderSentMail)
            Set Item.SaveSentMessageFolder = objFolder
        End If
    End If
    Set objFolder = Nothing
    Set objNS = Nothing
End Sub

Public Function IsInDefaultStore(objOL As Object) As Boolean
    Dim objApp As Outlook.Application
    Dim objNS As Outlook.NameSpace
    Dim objInbox As Outlook.MAPIFolder
    Dim blnBadObject As Boolean
    On Error Resume Next
    Set objApp = objOL.Application
    If Err = 0 Then
        Set objNS = objApp.Session
        Set objInbox = objNS.GetDefaultFolder(olFolderInbox)
        Select Case objOL.Class
            Case olFolder
                If objOL.StoreID = objInbox.StoreID Then
                    IsInDefaultStore = True
                Else
                    IsInDefaultStore = False
                End If
            Case olAppointment, olContact, olDistributionList, _
                 olJournal, olMail, olNote, olPost, olTask
                If objOL.Parent.StoreID = objInbox.StoreID Then
                    IsInDefaultStore = True
                Else
                    IsInDefaultStore = False
                End If
            Case Else
                blnBadObject = True
        End Select
    Else
        blnBadObject = True
    End If
    If blnBadObject Then
        'if cancel is selected then just leave in sent items, so do nothing.
'        MsgBox "This function isn't designed to work " & _
'               "with " & TypeName(objOL) & _
'                " objects and will return False.", _
'                , "IsInDefaultStore"
        IsInDefaultStore = False
    End If
    Set objApp = Nothing
    Set objNS = Nothing
    Set objInbox = Nothing
End Function

'modified from https://www.slipstick.com/developer/working-vba-nondefault-outlook-folders/
Function GetFolderFromPath(ByVal FolderPath As String) As Outlook.Folder
    Dim oFolder As Outlook.Folder
    Dim FoldersArray As Variant
    Dim i As Integer

    On Error GoTo GetFolderPath_Error
    If Left(FolderPath, 2) = "\\" Then
        FolderPath = Right(FolderPath, Len(FolderPath) - 2)
    End If
    'Convert folderpath to array
    FoldersArray = Split(FolderPath, "\")
    Set oFolder = Application.Session.Folders.Item(FoldersArray(0))
    If Not oFolder Is Nothing Then
        For i = 1 To UBound(FoldersArray, 1)
            Dim SubFolders As Outlook.Folders
            Set SubFolders = oFolder.Folders
            Set oFolder = SubFolders.Item(FoldersArray(i))
            If oFolder Is Nothing Then
                Set GetFolderFromPath = Nothing
            End If
        Next
    End If
    'Return the oFolder
    Set GetFolderFromPath = oFolder
    Exit Function

GetFolderPath_Error:
    Set GetFolderPath = Nothing
    Exit Function
End Function