Hi everyone,
Thanks for helping out here and for providing the bounces guide, @TomM2!
@MZS - I can see that you’re using a free HubSpot account, correct? I would be happy to investigate this for you if you could help me with a few details:
1) Are you seeing this bounce error only within HubSpot or are you also seeing it when you send an email outside of HubSpot?
2) Do you see this bounce error for only this particular email address or for any email address with your company’s domain?
As @TomM2 mentioned, you will need to work with your IT Team to prevent this from happening in the future, however, if there’s a bounce on our end, we may also be able to assist 
Thank you!
Looking forward to hearing from you!
Cheers,
Kristen