Hi I replied to a single email from within my local Mail client (Apple Mail) to a previous sender that I have not messaged before. Before sending I BCC’d my Hubspot account to track the conversation.
Shortly afterward I recieved a "Undelivered Mail Returned to Sender
notice" which began:
The mail system *******@bcc.hubspot.com: host mx.hubapi.com[**.***.***.**] said: *** *.*.* [ESA] Sender blocked.
Can anyone tell me what happended/how to rectify this please?
Hi @AndyHall,
Thank you for posting in our Community 
I found for you these 2 posts that can help you! This post “Undelivered cc mails to Hubspot” from @JessicaH and this post “Hubspot Message blocked” from @karstenkoehler.
If after following the steps indicated in these 2 posts you still have this behavior, can you please give some additional information?
The more info, screenshots, and details you can provide, the better the Community can assist.
I hope this helps!
Thanks and have a lovely day!
Bérangère
Hi Bérangère, thank you for your reply. It appears that the problem maybe that I was replying to a customer email newsletter. My guess is that this triggered a spam filter in Hubspot. When I tried sending to the same address directly afterwards no undelivered message was generated.