LINQ Lambda-Expression Diff

var groupedOccurences = occurences
                    .SelectMany(static occurence => occurence.MailAddress.Split(',', StringSplitOptions.RemoveEmptyEntries).Select(addr => new
                    {
                        MailAddress = addr.Trim(),
                        occurence.DatabasePath,
                        occurence.MaskName
                    }))
                    .GroupBy(static occurence => occurence);

var groupedOccurences = from occurence in occurences
                        from address in occurence.MailAddress.Split(',', StringSplitOptions.RemoveEmptyEntries)
                        group new {
                            MailAddress = address.Trim(),
                            occurence.DatabasePath,
                            occurence.MaskName
                        } by occurence into grp
                        select grp;