Outlook Group Emails Not Being Delivered via Gmail

I have set up numerous email groups in Outlook so I can send out monthly newsletters to my fan base. I used to send these group emails via Verizon with no problems. Now I have a Gmail account and every time I try to send an email to one of these groups they come back to me with a message stating, "Your message has been blocked by...." In fact, I included my own Gmail address in this group email, and my own Gmail account blocked it.

The Gmail Help Page offers so many choices as to why these emails were blocked, how is one to know what the real reason is?