locked questionbcc

Cherrill <cdjamieson@...>

One of my members and I each attempted to send an email via bcc. to our group here at groups.io and our group at yahoo groups.
The one which went to groups.io was rejected for both of us.  So both of us then sent them individually to groups.io and they were accepted. 
Is this something which isn't allowed by groups.io to receive an email from the bcc. line ???
Thank you

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