Tagging emails with categories without creating duplicate categories

Question

I am attempting to write a rule that applies a category to all incoming mail.

Ultimately I would like to use this to tag C and C++ related emails with a "Programming - C" and "Programming - C++" tags, but I simplified the example.

I also want to run this rule on mail that already has the specified categories, but I don't want it to double tag an email that is already tagged.

Here is the subroutine for adding a category without creating a duplicate:

' Add a category but don't create duplicates
Sub AddCategory(ByRef Item As MailItem, strCategory As String)
    Dim exists As Boolean
    Dim arrCategories As Variant
    
    ' Initialize variables
    exists = False
    arrCategories = Split(Item.categories, ",")
    
    ' Loop through all categories
    For i = LBound(arrCategories) To UBound(arrCategories)
    
        ' Check if the specified category already exists
        If StrComp(strCategory, arrCategories(i)) = 0 Then
            exists = True
            Exit For
        End If
    Next i

    ' If the category does not exist, add it
    If Not exists Then
        Item.categories = Item.categories & "," & strCategory
    End If
End Sub

The subroutine that calls it:

Sub filter(Item As MailItem)
    Call AddCategory(Item, "Programming - C")
    Call AddCategory(Item, "Programming - C++")
    Item.Save
End Sub

This filter subroutine is called from a rule and applies to all incoming mail.

If I run this rule on "All items in Inbox" and an email is already tagged with both "Programming -C" and "Programming - C++" it will duplicate the second tag.

So if "Programming - C" is the first tag it will duplicate "Programming - C++" and vice versa.

How can I check existing tags to avoid duplicates?

Answer 1

After figuring out how to use the VBA line by line debugger I eventually found the problem...

It turns out that Item.Categories returns the categories as a string in the format:

"Category1, Category2, ..."

Each category is separated by a comma and a space.

The solution was to change the line:

arrCategories = Split(Item.categories, ",")

to

arrCategories = Split(Item.categories, ", ")