Why would you want to concatenate the recipient list?
Once your email is created (this line)Code:Set aEmail = CreateItem(olMailItem)
You can add recipients individually; to use your example of taking address from "Sheet 1" within a range A1:A100. This short code creates a new message and populates the "to list"
You also noted errors (correctly identified by being caused as outlook library access). If you cannot establish a link to that library you can also use "late binding" and that link is no longer required.Code:Sub CreateMail() Dim WS As Worksheet, x As Long Dim ou As Outlook.Application Dim nEm As Outlook.MailItem Set ou = New Outlook.Application Set nEm = CreateItem(olMailItem) Set WS = ThisWorkbook.Sheets("Sheet1") For x = 1 To 100 nEm.Recipients.Add (WS.Range("A" & x).Value) Next nEm.Display End Sub
See this VBA references and early binding vs late binding | Excel Matters for more information