Symantec Email Proxy deleted an important e mail

I received today, for the first time, an e mail from Symantec Proxy stating that it had removed an e mail from a client.  I have received multiple e mails from this client in the past without any issues.

Here is the redacted e mail I received:

Symantec Email Proxy deleted the following email message:

From: "client name and e mail address>

To: "my name and e mail address>

Subject: RE: Approval of Permanent Employment Certification; next steps

What do I do to make sure this doesn't continue to occur?