What is 554 mail from sender rejected for policy reasons?

[ajitshukla61116]

Hi all, I am getting this error while trying to send email alert I don't what could be the reason for this.Please help me to resolve this issue.

Mail Server Settings:
[email]
auth_password =
auth_username =
mailserver = smtp.abc.com:25
pdf.header_left = none
pdf.header_right = none
use_ssl = 0
use_tls = 0
from = shukla.ajit007@abc.com

error code:

2019-05-02 12:10:05,545 +0530 ERROR sendemail:137 - Sending email. subject="Splunk Alert: internal", results_link="http://testinternal:8000/app/abc/search?q=%7Cloadjob%20scheduler__admin_eHczX3NvY19sNTNoX2Jpeg__internal_at_1556779200_27%20%7C%20head%201%20%7C%20tail%201&earliest=0&latest=now", recipients="[u'amit.tiwari@abc.com']", server="smtp.abc.com:25"
2019-05-02 12:10:05,546 +0530 ERROR sendemail:452 - (554, 'Mail from shukla.ajit007@abc.com rejected for policy reasons.', u'shukla.ajit007@abc.com') while sending mail to:amit.tiwari@abc.com

[richgalloway]

This is not a Splunk error. The sending email system blocked the message because it violated a local rule. Talk to your mail admin.