Один метод описан здесь .
sString = "my1@email.com xxx my2@email.com yyy my3@email.com"
asString = Split(sString, " ")
For i = 0 To UBound(asString)
If asString(i) Like "*@*.*" Then
sEmail = sEmail & "," & asString(i)
End If
Next
MsgBox Mid(sEmail, 2)