Warning: hostname localhost does not resolve to address

i'm using iRedmail on my Debian box. I tried to use outlook for for email client, but i got this error and couldn't resolve it.

Nov 19 17:25:10 mail postfix/smtpd[7011]: warning: hostname localhost does not resolve to address my-ip
Nov 19 17:25:10 mail postfix/smtpd[7011]: connect from unknown[my-ip]
Nov 19 17:25:15 mail postfix/smtpd[7011]: NOQUEUE: reject: RCPT from unknown[my-ip]: 504 5.5.2 <KevinNguyen>: Helo command rejected: need fully-qualified hostname; from=<postmaster@mydomain.com> to=<postmaster@mydomain.com> proto=ESMTP helo=<KevinNguyen>
Nov 19 17:25:15 mail postfix/smtpd[7011]: lost connection after RCPT from unknown[my-ip]
Nov 19 17:25:15 mail postfix/smtpd[7011]: disconnect from unknown[my-ip]

my /etc/hosts

### Hetzner Online AG installimage
# nameserver config
# IPv4
127.0.0.1 localhost.localdomain localhost mydomain.com mail
#::1            localhost.localdomain   localhost mail.mydomain.com mail
#127.0.0.1 www.itulan.dk
#127.0.0.1  Debian-70-wheezy-64-LAMP
#127.0.0.1 mail.mydomain.com mail
#
# IPv6
#::1 ip6-localhost ip6-loopback
#fe00::0 ip6-localnet
#ff00::0 ip6-mcastprefix
#ff02::1 ip6-allnodes
#ff02::2 ip6-allrouters
#ff02::3 ip6-allhosts
#2a01:4f8:b0:7eaf::2  Debian-70-wheezy-64-LAMP

and smtpd_helo_restrictions:

smtpd_helo_restrictions = permit_mynetworks reject_invalid_helo_hostname reject_non_fqdn_helo_hostname

My main.cnf

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# TLS parameters
smtpd_tls_cert_file = /etc/ssl/certs/iRedMail_CA.pem
smtpd_tls_key_file = /etc/ssl/private/iRedMail.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

myhostname = mail.mydomain.com
alias_maps = hash:/etc/postfix/aliases
alias_database = hash:/etc/postfix/aliases
myorigin = mail.mydomain.com
#myorigin = localhost
mydestination = $myhostname, localhost, localhost.localdomain, localhost.$myhostname
relayhost =
mynetworks = 127.0.0.0/8 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
home_mailbox = Maildir/

virtual_alias_maps = proxy:pgsql:/etc/postfix/pgsql/virtual_alias_maps.cf, proxy:pgsql:/etc/postfix/pgsql/domain_alias_maps.cf, proxy:pgsql:/etc/postfix/pgsql/catchall_maps.cf, proxy:pgsql:/etc/postfix/pgsql/domain_alias_catchall_maps.cf
home_mailbox = Maildir/
#inet_protocols = ipv4
#virtual_alias_domains =
allow_percent_hack = no
swap_bangpath = no
mydomain = mydomain.com
mynetworks_style = host
smtpd_data_restrictions = reject_unauth_pipelining
smtpd_reject_unlisted_recipient = yes
smtpd_reject_unlisted_sender = yes
smtpd_sender_restrictions = permit_mynetworks, reject_sender_login_mismatch, permit_sasl_authenticated
delay_warning_time = 0h
maximal_queue_lifetime = 4h
bounce_queue_lifetime = 4h
proxy_read_maps = $canonical_maps $lmtp_generic_maps $local_recipient_maps $mydestination $mynetworks $recipient_bcc_maps $recipient_canonical_maps $relay_domains $relay_recipient_maps $relocated_maps $sender_bcc_maps $sender_canonical_maps $smtp_generic_maps $smtpd_sender_login_maps $transport_maps $virtual_alias_domains $virtual_alias_maps $virtual_mailbox_domains $virtual_mailbox_maps $smtpd_sender_restrictions
smtp_data_init_timeout = 240s
smtp_data_xfer_timeout = 600s
smtpd_helo_required = yes
smtpd_helo_restrictions = permit_mynetworks reject_invalid_helo_hostname reject_non_fqdn_helo_hostname
queue_run_delay = 300s
minimal_backoff_time = 300s
maximal_backoff_time = 4000s
enable_original_recipient = no
disable_vrfy_command = yes
allow_min_user = no
message_size_limit = 15728640
virtual_minimum_uid = 2000
virtual_uid_maps = static:2000
virtual_gid_maps = static:2000
virtual_mailbox_base = /var/vmail
transport_maps = proxy:pgsql:/etc/postfix/pgsql/transport_maps_user.cf, proxy:pgsql:/etc/postfix/pgsql/transport_maps_domain.cf
virtual_mailbox_domains = proxy:pgsql:/etc/postfix/pgsql/virtual_mailbox_domains.cf
virtual_mailbox_maps = proxy:pgsql:/etc/postfix/pgsql/virtual_mailbox_maps.cf
sender_bcc_maps = proxy:pgsql:/etc/postfix/pgsql/sender_bcc_maps_user.cf, proxy:pgsql:/etc/postfix/pgsql/sender_bcc_maps_domain.cf
recipient_bcc_maps = proxy:pgsql:/etc/postfix/pgsql/recipient_bcc_maps_user.cf, proxy:pgsql:/etc/postfix/pgsql/recipient_bcc_maps_domain.cf
relay_domains = $mydestination, proxy:pgsql:/etc/postfix/pgsql/relay_domains.cf
smtpd_sender_login_maps = proxy:pgsql:/etc/postfix/pgsql/sender_login_maps.cf
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
broken_sasl_auth_clients = yes
smtpd_sasl_security_options = noanonymous
smtpd_sasl_authenticated_header = no
smtpd_recipient_restrictions = reject_unknown_sender_domain, reject_unknown_recipient_domain, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_unlisted_recipient, check_policy_service inet:127.0.0.1:7777, check_policy_service inet:127.0.0.1:10031, permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
smtpd_end_of_data_restrictions = check_policy_service inet:127.0.0.1:10031
smtpd_tls_security_level = may
smtpd_tls_loglevel = 0
smtpd_tls_CAfile = /etc/ssl/certs/iRedMail_CA.pem
tls_random_source = dev:/dev/urandom
mailbox_command = /usr/lib/dovecot/deliver
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1
smtpd_sasl_type = dovecot
smtpd_sasl_path = ./dovecot-auth
content_filter = smtp-amavis:[127.0.0.1]:10024
smtp-amavis_destination_recipient_limit = 1
#inet_protocols = ipv4
#virtual_alias_domains =
#inet_protocols = ipv4
#virtual_alias_domains =
#inet_protocols = ipv4
#virtual_alias_domains =
#inet_protocols = ipv4
#virtual_alias_domains =
inet_protocols = ipv4
virtual_alias_domains =