QRadar: Emails are not sent even if the email configuration is right and the test connection is successful

The following error can be seen in /var/log/maillog file, which indicates that the email delivery failed as the client does not have permissions to send as this sender:

Jun 15 09:03:49 Qradarhostname postfix/qmgr[4720]: 7EEDEC004EA: from=<QRADAR@localhost.localdomain>, size=24378, nrcpt=1 (queue active)
Jun 15 09:03:55 Qradarhostname postfix/smtp[120821]: 7EEZDE4EA: to=<abc@xyz.com>, relay=mail.xyz.com[XX.XX.XX.XX]:25, delay=5.6, delays=0.06/0.27/5.2/0.01, dsn=5.7.60, status=bounced (host mail.xyz.com[XX.XX.XX.XX] said: 550 5.7.60 SMTP; Client does not have permissions to send as this sender (in reply to end of DATA command))
Jun 15 09:03:55 Qradarhostname postfix/cleanup[120819]: 3A456C005CE: message-id=<20230605020355.3A456C005CE@Qradarhostname.xyz.com>
Jun 15 09:03:55 Qradarhostname postfix/bounce[121069]: 7EEZDE4EA: sender non-delivery notification: 3A456C005CE 

These errors are caused due to an incorrect value in the Alert Email From Address under Admin => System Settings.

To resolve these errors, perform following steps:

1. On the QRadar GUI, go to Admin tab => System Settings => Alert Email From Address
2. Correct the setting to reflect the email address that has permission to send emails (check with your email server's administrator for the correct email address)