Hello,
if I understand correctly the iRedMAil install script packages_freebsd.sh does the following with the Apache port:

WITH_APR_FROM_PORTS=true
WITH_THREADS=true
WITH_MYSQL=true
WITHOUT_PGSQL=true
WITHOUT_SQLITE=true
WITH_IPV6=true
WITH_BDB=true
WITH_AUTH_BASIC=true
WITH_AUTH_DIGEST=true
WITH_AUTHN_FILE=true
WITH_AUTHN_DBD=true
WITH_AUTHN_DBM=true
WITH_AUTHN_ANON=true
WITH_AUTHN_DEFAULT=true
WITH_AUTHN_ALIAS=true
WITH_AUTHZ_HOST=true
WITH_AUTHZ_GROUPFILE=true
WITH_AUTHZ_USER=true
WITH_AUTHZ_DBM=true
WITH_AUTHZ_OWNER=true
WITH_AUTHZ_DEFAULT=true
WITH_CACHE=true
WITH_DISK_CACHE=true
WITH_FILE_CACHE=true
WITH_MEM_CACHE=true
WITH_DAV=true
WITH_DAV_FS=true
WITH_BUCKETEER=true
WITH_CASE_FILTER=true
WITH_CASE_FILTER_IN=true
WITH_EXT_FILTER=true
WITH_LOG_FORENSIC=true
WITH_OPTIONAL_HOOK_EXPORT=true
WITH_OPTIONAL_HOOK_IMPORT=true
WITH_OPTIONAL_FN_IMPORT=true
WITH_OPTIONAL_FN_EXPORT=true
WITH_LDAP=true
WITH_AUTHNZ_LDAP=true
WITH_ACTIONS=true
WITH_ALIAS=true
WITH_ASIS=true
WITH_AUTOINDEX=true
WITH_CERN_META=true
WITH_CGI=true
WITH_CHARSET_LITE=true
WITH_DBD=true
WITH_DEFLATE=true
WITH_DIR=true
WITH_DUMPIO=true
WITH_ENV=true
WITH_EXPIRES=true
WITH_HEADERS=true
WITH_IMAGEMAP=true
WITH_INCLUDE=true
WITH_INFO=true
WITH_LOG_CONFIG=true
WITH_LOGIO=true
WITH_MIME=true
WITH_MIME_MAGIC=true
WITH_NEGOTIATION=true
WITH_REWRITE=true
WITH_SETENVIF=true
WITH_SPELING=true
WITH_STATUS=true
WITH_UNIQUE_ID=true
WITH_USERDIR=true
WITH_USERTRACK=true
WITH_VHOST_ALIAS=true
WITH_FILTER=true
WITH_VERSION=true
WITH_PROXY=true
WITH_PROXY_CONNECT=true
WITH_PATCH_PROXY_CONNECT=true
WITH_PROXY_FTP=true
WITH_PROXY_HTTP=true
WITH_PROXY_AJP=true
WITH_PROXY_BALANCER=true
WITH_SSL=true
WITH_SUEXEC=true
WITH_CGID=true

This enables all the Apache modules in the standard httpd.conf. I cannot imagine that all these modules are necessary for iRedMail to function properly.