Finally got it working with WebDAV. It would work too with MAPI but it's really long to reach a deep parent folder (going thru folder by folder each times).
Here is the function I got:
Public Function CreateFolderToLLFolder(parentId As String, folderName As String) As String
Dim dav As New ADODB.Record
Dim elements As ADODB.Recordset
Dim fields(1) As Variant
Dim values(1) As Variant
dav.Open URL_WEBDAV & parentId, "", adModeReadWrite, , , LLUser, LLPassword
Set elements = dav.GetChildren
fields(0) = "RESOURCE_PARSENAME"
values(0) = folderName
fields(1) = "RESOURCE_ISCOLLECTION"
values(1) = True
elements.addnew fields, values
elements.Close
Set elements = dav.GetChildren
dav.Close
elements.MoveFirst
Do Until elements.EOF
If elements("RESOURCE_DISPLAYNAME") = folderName Then
Exit Do
End If
elements.MoveNext
Loop
If Not elements.EOF Then
dav.Open elements
CreateFolderToLLFolder = dav("urn:x-opentext-com:ll:properties:nodeid")
Else
CreateFolderToLLFolder = -1
End If
dav.Close
elements.Close
Exit Function
URL_WEBDAV is for example http://livelink.yourserver.com/livelinkdav/nodes/
. Also use LLUser
and LLPassword
if needed.