Mail Rejected by Keyword

I received complaint from user that her mail was rejected by the receiver mail server.

The massages from mail server are:

Subject: Undelivered Mail Returned to Sender
This is the mail system at host mxwcom.263xmail.com.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report.
You can delete your own text from the attached returned message.
The mail system
: host mxcom.263xmail.com[211.150.64.38] said:
mail rejected by keyword (in reply to end of DATA command)

Referring to that message I conclude that the content of email from the user contain keyword that is usually use by spam email. Then I checked the content of email and I found keyword "offering price" in the message.

I asked to the user to change keyword "offering price" in her email and resend the email to the recipient.

After changing "offering price" words with "quotation" and resending the email, then the email was sent successfully and no rejection from recipient email server.