Hi Eunice,
Good day. I'm Jhun an independent advisor. Your Outlook issue seems disappointing specially you've been sending newsletter mail for the past 10 years without issue. This is likely running into Microsoft's outbound anti-spam limits and not a content issue since you said that it works when you split the list in half, You BBC 49 people and you're using Classic Outlook. That suggests that you're hitting a recipient limit or spam threshold trigger.
You can try this alternate procedure and let's see if it will solve the problem.
- In your Classic Outlook go to People.
- Create New Contact Group.
- Add your members.
- Send to the group name (NOT BCC).
- Still subject to limits, but less likely to trigger spam than large BCC.
I hope this helps.
Regards,
Jhun