Skip already categorized mails - vba

Question

Current Code:
Dim outlookapp
Dim olns As Outlook.Namespace
Dim Fldr As Outlook.MAPIFolder
Dim olMail As Object
'Dim olMail As Outlook.MailItem
Dim myTasks
Dim projIDsearch As String
Dim myrecipient As Outlook.Recipient
Dim daysAgo As Long
Set outlookapp = CreateObject("Outlook.Application")
Set olns = outlookapp.GetNamespace("MAPI")
Set myrecipient = olns.CreateRecipient("Ccbcphelpdesk")
myrecipient.Resolve
'Set Fldr = olNs.GetDefaultFolder(olFolderInbox).Folders("ExemptionReview")
Set Fldr = olns.GetSharedDefaultFolder(myrecipient, olFolderInbox)
' Restrict search to daysAgo
daysAgo = 0
Set myTasks = Fldr.Items.Restrict("[ReceivedTime]>'" & Format(Date - daysAgo, "DDDDD HH:NN") & "'")
projIDsearch = ActiveCell.Cells(1, 4)
For Each olMail In myTasks
If (InStr(1, olMail.Subject, projIDsearch, vbTextCompare) > 0) Then
olMail.Categories = "ESP"
olMail.Save
End If
Next
end sub
This looks up emails pertaining to a search string in the subject then tags them as ESP. I need to skip emails that are already categorized.
I have tried:
If (InStr(1, olMail.Subject, projIDsearch, vbTextCompare) > 0) Then
If olmail.categories Is nothing then 'line returns and error 424
olMail.Categories = "ESP"
olMail.Save
End If
End If
How can I skip Emails that are already categorized and only categorize emails with no category?

Answer 1

https://msdn.microsoft.com/en-us/library/office/ff860423.aspx
Categories is a String-type property, so test with something like:
If Len(olmail.Categories) = 0 Then

Answer 2

Use Logical Operators And Not on your Restrict method
Set myTasks = Fldr.Items.Restrict("[ReceivedTime]>'" & Format(Date - daysAgo, "DDDDD HH:NN") & "' And Not [Categories] = 'ESP'")
and remove your If olmail.categories Is nothing that way your not checking every olmail- and it should speedup your loop