If this happens then check the Application Event Log. If you see the message below then you need to change your registr settings

MAPISendMail: Failed to submit message. Attachments to the message exceeded the size limit set by your Administrator.

Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences

If there is a Key called MaxiumAttachmentSize then delete it or enter a value of 1000+. Setting it to zero appears to cause this error. 

Helpfull link: https://support.microsoft.com/en-ca/help/2813269/attachment-size-exceeds-the-allowable-limit-error-when-you-add-a-large 

I would recommend disabling the iCloud Outlook Add-in by going to File > Options > Add-Ins, and then going into "COM Add-ins" to uncheck that item and disable it.  

https://www.sitepoint.com/outlook-unblock-unsafe-attachments/

There’s a vast range of desktop and online email clients but it’s hard to beat Microsoft Outlook. The application has been around since 1997 and, despite a few dodgy decisions regarding HTML rendering, it’s still the email client of choice for me and many others.

Unfortunately, there’s an Outlook message web developers hate:

Outlook blocked access to the following potentially unsafe attachments…

Thanks Microsoft. I know why you’re blocking that JavaScript file, but I know what it is and I really, really want it.

Outlook doesn’t allow you to unblock unsafe attachments. Fortunately, there is a way to obtain the file and prevent the embarrassment of requesting a renamed version. Before we start…

Still here? OK, here’s what you do:

1. Close Outlook

2. Run regedit.exe
Navigate to:

HKEY_CURRENT_USERSoftwareMicrosoftOfficeXX.XOutlookSecurity

Where XX.X indicates your version of Outlook:

• 14.0 for Microsoft Office 2010
• 12.0 for Microsoft Office 2007
• 11.0 for Microsoft Office 2003
• 10.0 for Microsoft Office 2002
• 9.0 for Microsoft Office 2000

3. Create a new value
Create a new string value key in that location named:

Level1Remove

4. Choose your ‘safe’ file types
Edit the key and enter a list of attachment extensions you want to unblock. Each should start with a period and be separated with a semi-colon. For example…

To unblock JavaScript files only, enter:

.js

To unblock JavaScript, VBScript, and exe files, enter:

.js;.vbs;.exe

Click OK to save the value then exit regedit.

5. Restart Outlook
The attachment should be magically unblocked. Try rebooting if that’s not the case.

Here is some code for exporting your Outlook Notes.

Sub NotesToRTF()
    Dim myNote As Variant
    Dim cnt As Integer
    Dim noteName As String
    Dim strExportFolder As String
   
    strExportFolder = "C:\Notes-RTF\"
   
    If Dir(strExportFolder, vbDirectory) = "" Then
        MkDir strExportFolder
    End If
   
    Set myNote = Application.GetNamespace("MAPI").PickFolder
    For cnt = 1 To myNote.Items.Count
        noteName = Trim(Replace(Replace(Replace(Replace(myNote.Items(cnt).Subject, "/", "-"), "\", "-"), ":", ""), vbTab, ""))
        Debug.Print noteName
        myNote.Items(cnt).SaveAs strExportFolder & noteName & ".rtf", OlSaveAsType.olRTF
    Next
   
    Shell "C:\WINDOWS\explorer.exe """ & strExportFolder & "", vbNormalFocus
End Sub

Sub NotesToText()
    Dim myNote As Variant
    Dim cnt As Integer
    Dim noteName As String
    Dim strExportFolder As String
   
    strExportFolder = "C:\Notes-Text\"
   
    If Dir(strExportFolder, vbDirectory) = "" Then
        MkDir strExportFolder
    End If
   
    Set myNote = Application.GetNamespace("MAPI").PickFolder
    For cnt = 1 To myNote.Items.Count
        noteName = Trim(Replace(Replace(Replace(Replace(myNote.Items(cnt).Subject, "/", "-"), "\", "-"), ":", ""), vbTab, ""))
        Debug.Print noteName
        myNote.Items(cnt).SaveAs strExportFolder & noteName & ".txt", OlSaveAsType.olTXT
    Next
   
    Shell "C:\WINDOWS\explorer.exe """ & strExportFolder & "", vbNormalFocus
End Sub

Hope it helps someone else out there.