ZoHo Group does not forward to Yahoo email addresses (inconsistent)

ZoHo Group does not forward to Yahoo email addresses (inconsistent)

I have a mail group set up in Zoho.  If I send to this group (e.g. test@denverreformed.com) from my admin zoho account (e.g. admin@denverreformed.com) the email correctly gets forward to ALL members of the group (including yahoo addresses).  However, if I send to the group from a non zoho account (e.g my personal gmail or work emails), then the yahoo email addresses do not get forwarded the email!  

I can't figure out what is going on.  It seems to be a problem with zoho due the inconsistent behavior described above.  

Anyone else experiencing this?

Resolution?