Step1: Login to WHM.
Step2: Under Security Center.
Step3: Click SMTP Restrictions (allow only the MTA, mailman, and root to connect to remote SMTP servers).
Step1: Login to WHM.
Step2: Under Security Center.
Step3: Click SMTP Restrictions (allow only the MTA, mailman, and root to connect to remote SMTP servers).
Step4: Click Disable.