501 Malformed HELO error during smtp troubleshooting via telnet

I've got some emails bouncing back from specific internet recipients, so I decided to do the old "telnet to the email server on port 25" testing routine.

I get connected fine, but when I enter either helo or ehlo I get "501 Malformed HELO" (or EHLO...I tried both).

I thought this was strange, but I tried the same thing with our own domain and got the same response.  Note that both we and the problem recipients use MXlogic, now MacAffee, as email proxies to filter spam (it's a paid service).

We're lhshealth.com, the recipient domain is cambridgecap.com.  DNS looks okay to me, and I've checked all the usual stuff...the address is correct if you do a reverse lookup on mail.lhshealth.com, and Exchange is sending mail.lhshealth.com in its banner.  I did all my testing from CMD prompts on our Exchange box.

Anyone know what these errors mean?
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if you try HELO {the FQND of your SMTP server}, you will probably find it will work (i.e. HELO smtp.lhshealth.com)

A lot of SMTP servers expect the calling servers to identify themselves as part of HELO.

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ZipoBibrock5e8Author Commented:
That was indeed the case.  As an SMTP amateur I'd never seen that before.
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