Me again - sorry! After Bluehost lifted the spam filter last night I was able to send emails. I successfully sent two emails this morning - one to share a blog post, one the second to share a blog page. When I went to share another blog page after that, it wouldn't send. I tried a test message several times and it wouldn't send. I deactivated and reactivated the plugin and still doesn't send.
I called Bluehost and they confirmed there is no block on their end. They also looked at the logs and the activity of me trying to send those emails doesn't even show up - the last thing they can see are the 2 emails sent successfully earlier this morning.
The also confirmed there is no max limiting my sending, as I can send up to 100 emails per hour and I'm merely sending a few a day.
So, still stuck on why I can't send - any ideas? Many thanks for the help.