exim - EXIM4 configuration directives: .ifdef, ifndef -

all!

i'm configuring exim mail-server , i'm newbie it. not first mail server configuration, first of exim.

so far, have read different config docs (e.g. this one) in internet , exim's configuration manual, well. , more clear me. 1 issue not clear yet - concerned .ifdef, .ifndef directives.
example,

.ifdef check_mail_helo_issued   deny     message = no helo given before mail command     condition = ${if def:sender_helo_name {no}{yes}} .endif 

far saw manual, clause means if macros check_mail_helo_issued declared, followed actions applied. if not present anywhere, actions not applied.
, if want apply acl (it part of acl), better use without .ifdef directive.

so, please, correct me if i'm wrong,

you either delete .ifdef , .endif directives or define check_mail_helo_issued = yes somwhere logically 'before' deny statement.