How can I automate the splitting of this Excel 2007 worksheet?

I have just started to make use of the services of a bulk mail provider called Your Mailing List Provider (YMLP) and have hit the problem that YMLP will reject any attempts to import a contact record containing an email address that is already present in an existing contact record (even though the names are different).

However, I need to issue personalised emails to people who may share the same email address (which is not an unusual situation). The only way round this problem is for me to separate such contact records so that they are uploaded to different 'contact groups' in YMLP.

For example, consider the following Excel worksheet:

Email                                    FirstName  LastName  UserName
joe@hotmail.com              Joe             Bloggs       JB999
joe@hotmail.com              Jane           Bloggs        janeyB

jim@yahoo.co.uk              James         Smith         Jimmy3
jim@yahoo.co.uk              Susan         Smith         Sue2

thebrowns@nowhere.net   John           Brown         jonny
thebrowns@nowhere.net   Mary          Brown         mary17
thebrowns@nowhere.net   Jack           Brown         jackthelad

fred@hotmail.com             Fred          Green         elvis
fred@hotmail.com            Judy           Green         knitter

kittensrus@cat.com          Liza          Pawse         purrs1
kittensrus@cat.com          Mark         Pawse         purrs2
kittensrus@cat.com          Timothy    Pawse         purrs3
 
I would want to split that into three separate worksheets, as follows:

GROUP 1
Email                                  FirstName  LastName  UserName
joe@hotmail.com             Joe            Bloggs       JB999
jim@yahoo.co.uk             James        Smith         Jimmy3
thebrowns@nowhere.net  John          Brown         jonny
fred@hotmail.com           Fred           Green         elvis
kittensrus@cat.com         Liza           Pawse        purrs1

GROUP 2
Email                                  FirstName  LastName  UserName
joe@hotmail.com            Jane           Bloggs        janeyB
jim@yahoo.co.uk            Susan         Smith         Sue2
thebrowns@nowhere.net  Mary          Brown        mary17
fred@hotmail.com           Judy           Green         knitter
kittensrus@cat.com         Mark          Pawse        purrs2

GROUP 3
Email                                  FirstName  LastName  UserName
thebrowns@nowhere.net  Jack           Brown        jackthelad
kittensrus@cat.com         Timothy      Pawse       purrs3


I would appreciate some guidance on how such a split might be achieved semi-automatically using Excel 2007.

David