Please note: This code utilizes the Microsoft VBScript Regular Expressions 5.5 library (enable it using the Tools- References dialog in the VBA IDE).

Create a VBA module and name it winapi_folderbrowser. Paste the following code into the new module:

""" BEGIN CODE
Private Const BIF_RETURNONLYFSDIRS As Long = &H1
Private Const BIF_DONTGOBELOWDOMAIN As Long = &H2
Private Const BIF_RETURNFSANCESTORS As Long = &H8
Private Const BIF_BROWSEFORCOMPUTER As Long = &H1000
Private Const BIF_BROWSEFORPRINTER As Long = &H2000
Private Const BIF_BROWSEINCLUDEFILES As Long = &H4000
Private Const MAX_PATH As Long = 260
Type BrowseInfo
hOwner As Long
pidlRoot As Long
pszDisplayName As String
lpszINSTRUCTIONS As String
ulFlags As Long
lpfn As Long
lParam As Long
iImage As Long
End Type
Type SHFILEOPSTRUCT
hwnd As Long
wFunc As Long
pFrom As String
pTo As String
fFlags As Integer
fAnyOperationsAborted As Boolean
hNameMappings As Long
lpszProgressTitle As String
End Type
Declare Function SHGetPathFromIDListA Lib "shell32.dll" ( _
ByVal pidl As Long, _
ByVal pszBuffer As String) As Long
Declare Function SHBrowseForFolderA Lib "shell32.dll" ( _
lpBrowseInfo As BrowseInfo) As Long
Function BrowseFolder(Optional Caption As String = "") As String
Dim BrowseInfo As BrowseInfo
Dim FolderName As String
Dim ID As Long
Dim Res As Long
With BrowseInfo
.hOwner = 0
.pidlRoot = 0
.pszDisplayName = String$(MAX_PATH, vbNullChar)
.lpszINSTRUCTIONS = Caption
.ulFlags = BIF_RETURNONLYFSDIRS
.lpfn = 0
End With
FolderName = String$(MAX_PATH, vbNullChar)

ID = SHBrowseForFolderA(BrowseInfo)

If ID Then
Res = SHGetPathFromIDListA(ID, FolderName)
If Res Then
BrowseFolder = Left$(FolderName, InStr(FolderName, vbNullChar) - 1)
End If
End If
End Function
''' END CODE

Create a new VBA module and name it mymacros. Paste the following code into the new module:

''' BEGIN CODE
Sub SaveMsgToFolderWithSubjectAndTimestamp()
Dim Item As MailItem
Dim strTargetFilename As String
Dim strTargetPath As String
Dim objRegExp As New RegExp
With objRegExp
.Global = True
.IgnoreCase = True
.Pattern = "[^\w+]"
End With
strTargetPath = BrowseFolder
Dim SelectedItems As Selection
Set SelectedItems = Outlook.ActiveExplorer.Selection
For Each Item In SelectedItems
strTargetFilename = objRegExp.Replace(Item.Subject, "_") + "_" + Format(Item.ReceivedTime, "yyyy_mm_dd_hhnnss")
Item.SaveAs strTargetPath + "\" + strTargetFilename + ".msg", olMSG
Next Item
End Sub
''' END CODE

Assign the macro SaveMsgToFolderWithSubjectAndTimestamp to a custom toolbar button and you’re all set.

One step further: Save attachments!

The code has been extended as follows: If message has attachments, a new folder is created, named according to the message subject, with “_ATTACHMENTS” appended, and all attachments are saved in the new folder.

Sub SaveMsgToFolderWithSubjectTimestampAttachments()
 Dim Item As MailItem
 Dim strTargetFilename As String
 Dim strTargetPath As String
 Dim Atmt As Attachment
 Dim strTargetAttachmentsFolderPath As String

 Dim objRegExp As New RegExp
 With objRegExp
 .Global = True
 .IgnoreCase = True
 .Pattern = "[^\w+]"
 End With

 strTargetPath = BrowseFolder

 Dim SelectedItems As Selection
 Set SelectedItems = Outlook.ActiveExplorer.Selection
 For Each Item In SelectedItems
 strTargetFilename = objRegExp.Replace(Item.Subject, "_") + "_" + Format(Now(), "yyyy_mm_dd_hhnnss")
 Item.SaveAs strTargetPath + "\" + strTargetFilename + ".msg", olMSG
 If Item.Attachments.Count > 0 Then
 ' Create new folder
 strTargetAttachmentsFolderPath = strTargetPath + "\" + strTargetFilename + "_ATTACHMENTS"
 MkDir strTargetAttachmentsFolderPath
 ' Save Attachments
 For Each Atmt In Item.Attachments
 Atmt.SaveAsFile strTargetAttachmentsFolderPath + "\" + Atmt.DisplayName
 Next Atmt
 End If
 Next Item
End Sub

Adding the following fixed the issue:
<meta http-equiv="X-UA-Compatible" content="IE=100" />

Here’s the detailed explanation:
MSDN Article

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