That would be the most likely case, @JenniferH15 .
It'd likely be worth working with those individuals to make sure your emails are absolutely safelisted in their setups. But most importantly, you'd want to work with their IT teams (if applicable) to make sure our domains are safelisted in their security programs.
The authentication tends to play a pretty big part as discussed earlier. Authenticating through us can help deliverability greatly, especially if you don't have your own domain / use a free email service. However if you have your own domain, then self-authentication will have the best results, especially when dealing with more stringent security programs.
Click here for an overview on authentication and links to help set up either type
It will also depend on the bounce. We rely on the receiving servers to provide us with accurate, recognizable codes to ensure you're being given accurate reporting on bounce types. If you're seeing odd discrepancies between your ability to directly email some contacts, and varying bounces when trying to send your e-blasts and newsletters to those same contacts, it'd definitely be worth reaching out to the Deliverability team to see what specialized advice they can provide.
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