I have one small issue trying to send out an group email to 265 parents. It won't go.
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Several things could be at fault.

1. You could have misspelled email addresses in your outgoing list. That could prevent the entire list from going out.
2. Your ISP might be considering anything over 30 recipients as potential spam and blocking such a large outgoing email group.

The easiest way around this is to use a service like MailChimp. It’s free up to around 2000 recipients.