Hi Michelle,
It appears your site is listed a on spam blacklist with Barracuda which could be causing the issue
https://mxtoolbox.com/SuperTool.aspx...k&run=toolpage
However, if you look at Barracuda by entering your domain name its not showing as blacklisted which is strange
https://www.barracudacentral.org/lookups
In the first instance I would report the issue to Barracuda by telling them mxtoolbox.com reports your site as being on Barracuda blacklist and ask them to investigate
https://www.barracudacentral.org/report
You could be on the blacklist due the number of e-mails sent in one go or it could be another site on the same IP address. I would also suggest you email BP to see if they can help further.
Sorry thats all the help I can offer with my limited knowledge.