Postfix - Server or Domain name not found

Question

I'm trying to configure my Postfix on my linux server but when I've tried to send test email it is generating the following error posted below. Can anyone help me with this ? I will be really grateful.

Here is my main.cf:

smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)
biff = no

append_dot_mydomain = no

readme_directory = no

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.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

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = instance-1
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = instance-1.c.test-72e61.internal, localhost.c.test-72e61.internal, localhost
relayhost = [smtp.c.test-72e61.internal]
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = + .
inet_interfaces = all

---

Dec 18 10:03:56 instance-1 postfix/qmgr[30463]: CF257675A6: from=<swdowiarz@instance-1.c.test-72e61.internal>, size=408, nrcpt=1 (queue active)

    Dec 18 10:03:56 instance-1 postfix/qmgr[30463]: 397F5675B3: from=<swdowiarz@instance-1.c.test-72e61.internal>, size=414, nrcpt=1 (queue active)

    Dec 18 10:03:56 instance-1 postfix/smtp[31477]: warning: relayhost configuration problem

    Dec 18 10:03:56 instance-1 postfix/smtp[31476]: warning: relayhost configuration problem

    Dec 18 10:03:56 instance-1 postfix/smtp[31476]: CF257675A6: to=<swdowiarz@groupon.com>, relay=none, delay=239771, delays=239770/0.01/0.02/0, dsn=4.3.5, status=deferred (Host or domain name not found. Name service error for name=smtp.c.test-72e61.internal type=AAAA: Host not found)

    Dec 18 10:03:56 instance-1 postfix/smtp[31477]: 397F5675B3: to=<wdowiarzsebastian@gmail.com>, relay=none, delay=239658, delays=239658/0.01/0.01/0, dsn=4.3.5, status=deferred (Host or domain name not found. Name service error for name=smtp.c.test-72e61.internal type=AAAA: Host not found)