Import Excel and Sort by eMail-Domain

PaddyB Connect to the CSV file with PowerQuery (PQ), do some transformations, sort and load back to Excel. Sound easy! And it is, though, you need to learn the basics of PQ first. The link below would be a good starting point.

https://exceloffthegrid.com/power-query-introduction/ 

You might need to use a macro to create the worksheet based on unique domain names. And then another macro to copy the relevant data for the domain names. You might need to separate the domain name from the email addresses first. Something like this will help:
RIGHT(A1,LEN(A1)-FIND("@",A1,1))
Once you separate the names, macro can do the rest.

Side note: If I were to do the work, I would not create separate sheets for each domain. I would lump them in one formatted table and filter them to display only those I need to work on.

I interpret 'lot of domains' as between 4 and 100 and assume that quite a few of them are new from month to month.
As described 26 Dec 2021 10:24 AM above, the attached file calculates the domains in the input addresses. Column A may be pasted or loaded via Data: (Get & Transform): From Text/CSV.

__/ Sheet3 has one of the domains entered into A1 and uses FILTER to fetch the addresses in that domain.

A3:

=FILTER(Input!A:A;IFERROR(FIND("@"& A1;Input!A:A);0))

__/ The first sheets;

• Column A shows the sheets in the workbook
• Column B shows the value in each sheets cell A1 (as chosen in C2)
• Column H shows the domains that not yet have its own sheet
  It is calculated by comparing column B with hidden column F (press Ctrl+8 to show its [+])

Click the button to generate the missing sheets.

__/ The macro will generate sheets for each missing domain as follows:

Sub domains2sheets()
    While Not IsError(Range("domains_without_sheet").Value)
        Sheets(Sheets.Count).Select
        If Not Range("a1").Value Like "?*.?*" Then
            MsgBox "Last sheet seems to not be a valid template?"
            Exit Sub
        Else
            Sheets(Sheets.Count).Copy After:=Sheets(Sheets.Count)
            Sheets(Sheets.Count).Name = "Sheet" & Sheets.Count
            Range("a1").Value = Range("domains_without_sheet").Value
        End If
    Wend
    Sheets(1).Select
End Sub

The defined name domains_without_sheet refers to =PowerPage!$H$2

Row 9 could just as well be 

Sheets(Sheets.Count).Name = Range("domains_without_sheet").Value

but would be misleading if cell A1 is changed.

Since it's just once a month, I think a paste and a click could be automatic enough.

It is also possible to select sheet4 and Shift+click the last sheet and delete them to only have the current months domains.

For this purpose or rather to get an overview of the number of items in each domain, I also added a counter in PowerPage!D:D. Minus one to exclude the sheets title.