Softbounce, flagged as a distribution list.

We have newsletter emails, going to an enterprise partner that are to a relatively small group of individuals who signed up for it. These are not customer facing, but partner to partner communications.

The email domain is not blocked, but the emails are soft bouncing and no one is receiving them at the server level. Upon looking to see if the domain was blocked, the enterprise webserver admin said that the emails are tripping a flag as a "distribution list."

Is this a concern others have had?

Is there a simple test for this?

Is there a good solution?

Thank you in advance for any suggestions you may have or experiences shared.