A member's email won't send to our club's members distlist.

Our FTH website:   airlinetrail.toastmastersclubs.org/
One of our club members, liz@liztrendowski.com, is trying to send our club newsletter to all our members at members-6976@toastmastersclubs.org.
The email get's sent from her Outlook OK, but she gets the following error message back:
       A message that you sent could not be delivered to one or more of    its recipients. This is a permanent error.
       The following address failed:     This email address is being protected from spambots. You need JavaScript enabled to view it.:
       multiple delivery attempts failed
I checked to make sure her email address is listed correctly in our members list, and it is.
Other members, including me, are using this members-6976@toastmastersclubs.org distlist just fine.
What are we doing wrong?  Thanks for any help you can provide.
 

Make sure that she doesn't have anything in the BCC box.

If not, ask her to send a test email with no attachments (maybe just send it to officers-6976@toastmastersclubs.org) 
 

one of the email addresses her email services uses was blocked please have her try again.

She tried again last night.  Same error message.  She is not using the BCC field and last night's test message had no attachments.  What's next?

What does "one of the email addresses her email services uses was blocked" mean?  Blocked by who/what?

She uses a hosting service that allows spammers to use their email service and the email server IP was blocked.
We are not blocking the 2 IP addresses that her service identifies as her MX records 74.208.5.3 and74.208.5.21

I see no email hitting the FTH server in the last 4 weeks. If she has another email address she could have that added as her secondary email and use that.