Email handshake with Verizon mail

I have been getting reports from verizon/mac users that mail is being rejected by my mail server.  I have many hundreds of folks who use Verizon and Frontier

It appears to be the HLO command which varies from the HELO command.  Here is the detailed reject notice:


Date: May 17, 2016 at 3:26:14 PM EDT

To: {edited for privacy}

Subject: Delivery Notification: Delivery has failed

This report relates to a message you sent with the following header fields:

 Message-id: <>

 Date: Tue, 17 May 2016 15:26:14 -0400

 From: Kim Barley <{edited for privacy}>

 To: {edited for privacy}

 Subject: test

Your message cannot be delivered to the following recipients:

 Recipient address: {edited for privacy}

 Reason: Server rejected MAIL FROM address.

 Diagnostic code: smtp;502 5.5.1 Command unrecognized: "HLO"

 Remote system: dns; (TCP||47606||25) ( ESMTP Merak 4.2.3; Tue, 17 May 2016 14:26:15 -0500)