Why is email I send to plug from gmail not delivered?

[Josef Lowder]

.
Why is email that I send to plug from gmail not delivered? 

Yesterday, I sent an email message to plug from gmail and 
it never did show up.  Today, I tried again, sending the 
message shown below, and it also has not been delivered. 

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from	Josef Lowder <joe at actionline.com> hide details 9:39 am
to	plug-discuss at lists.plug.phoenix.az.us
date	Jun 4, 2008 9:39 AM
subject	test only
mailed-by - gmail.com
Wednesday, June 4, 2008 at 9:40 am
Just testing to see if this message gets delivered to plug.
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Other email messages that I have sent from my new gmail 
account are apparently being delivered, so why do messages 
to plug not get delivered and/or posted?