Proper indexing of a table give the queries listed
CREATE TABLE [dbo].[Users](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [Email] [varchar](128) NOT NULL,
    [CreatedAt] [datetime] NOT NULL,
    [SourceId] [int] NOT NULL
PRIMARY KEY CLUSTERED
(
    [Id] ASC
) WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF,  ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

SELECT * FROM Users WHERE Email = 'some@email.com'
SELECT * FROM Users WHERE Email = 'some@email.com' AND SourceId = some integer
SELECT * FROM Users WHERE CreatedAt BETWEEN '2011-10-01' AND '2011-10-30'
SELECT * FROM Users WHERE CreatedAt BETWEEN '2011-10-01' AND '2011-10-30' AND SourceId = some integer

CREATE INDEX IX_Users_Email_SourceId ON Users (Email, SourceId)
CREATE INDEX IX_Users_CreatedAt ON Users (CreatedAt)
CREATE INDEX IX_Users_SourceId ON Users (SourceId)

WHERE Email = 'some@email.com'
index: Email
or Email, SourceId

WHERE Email = 'some@email.com' AND SourceId = some integer
index: SourceId, Email
or Email, SourceId

WHERE CreatedAt BETWEEN '2011-10-01' AND '2011-10-30'
index: CreatedAt
or CreatedAt, SourceId

WHERE CreatedAt BETWEEN '2011-10-01' AND '2011-10-30' AND SourceId = some integer
index: SourceId, CreatedAt
or CreatedAt, SourceId