Amazon SES connection error - "Authentication Credentials Invalid"

I had setup a fresh EC2 instance with postfix service, configured to send mails via SES . But it fails send mail and shows authentication failure as error in the mail log. Log is attached below :

Jun 20 18:35:44 test postfix/smtp[9518]: 9264412CE2D: to=<test@domain.hosting >, relay=email-smtp.eu-central-1.amazonaws.com[18.197.243.159]:587, delay=3.5, delays=0.06/0/3.4/0, dsn=4.0.0, status=deferred (SASL authentication failed; server email-smtp.eu-central-1.amazonaws.com[18.197.243.159] said: 535 Authentication Credentials Invalid)

I was able to send mail from the same EC2 instance by using SES of a different AWS account.

Both these accounts were configured the same way, with same policies. But still the mails send via the SES service on this AWS account fails.

So I doubt the emails send out from this AWS account is being blocked by AWS. Can anyone please let me know your thoughts and any solutions/suggestions on the same ?