Gmail/Google doesn’t like if you copy and paste email addresses into the CC or BCC lines. Please use this method instead.
Send bulk messages using Groups
Applies if you’re sending a message to a large group
If you’re sending a message to a large number of recipients, our system might flag the message as spam. The most common issue is that a message is Cc’d or Bcc’d to a large number of recipients, similar to how spam is sent out. To fix this, put all your recipients in a group and send the message to the group address instead. See Set up Groups for your team
Important: If a message can’t be delivered to a large number of the group’s members, the group message will bounce. Be sure to only include active, correctly spelled email addresses.