Debian 10 (Buster) - Postfix SMTP relay error for outgoing mail

Hello members

System: Server: debian 10 (Buster)

I am trying to configure my debian server with postfix to relay my server mails through mail.gmx.com to another email id.

I have the following error shown in the Log file /var/log/mail.log

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Sep 16 19:43:00 linga postfix/pickup[8674]: AEEC3E60CB4: uid=1000 from=<usr1@linga.com>
Sep 16 19:43:00 linga postfix/cleanup[8797]: AEEC3E60CB4: message-id=<20190916174300.AEEC3E60CB4@linga.com>
Sep 16 19:43:00 linga postfix/qmgr[8675]: AEEC3E60CB4: from=<usr1@linga.com>, size=339, nrcpt=1 (queue active)
Sep 16 19:43:00 linga postfix/cleanup[8797]: B8ADFE60CB3: message-id=<20190916174300.AEEC3E60CB4@linga.com>
Sep 16 19:43:00 linga postfix/local[8799]: AEEC3E60CB4: to=<root@linga.com>, relay=local, delay=0.1, delays=0.06/0.01/0/0.03, dsn=2.0.0, status=sent (forwarded as B8ADFE60CB3)
Sep 16 19:43:00 linga postfix/qmgr[8675]: B8ADFE60CB3: from=<usr1@linga.com>, size=460, nrcpt=1 (queue active)
Sep 16 19:43:00 linga postfix/qmgr[8675]: AEEC3E60CB4: removed
Sep 16 19:43:00 linga postfix/error[8800]: B8ADFE60CB3: to=<Notice.Server@gmail.com>, orig_to=<root@linga.com>, relay=none, delay=0.07, delays=0.03/0.01/0/0.03, dsn=4.7.5, status=deferred (delivery temporarily suspended: Cannot start TLS: handshake failure)
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The /etc/postfix/main.cf - entries are as follows:

************* /etc/postfix/main.cf ***************
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = linga.com
mydomain = linga.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
#myorigin = /etc/mailname
myorigin = $mydomain
mydestination = $myhostname, $mydomain, linga.com, localhost, localhost.$mydomain

********** Relay Info********
relayhost = [mail.gmx.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_tls_wrappermode = yes
smtp_tls_security_level = encrypt
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
*************************************************
I have also configured /etc/postfix/sasl_passwd
with [mail.gmx.com]:587 username:password

However, I am getting the following error message, have also tried with port 465, does not work as well.

Thanks in anticipation of your support.

Cheers.