I am having the same issue, mainly off of forms that are sent to me via a shared mailbox (hello@). When I attempt to forward them, they are sent back to the hello@ distribution list, and any additional text or commentary I entered in the draft is removed. Please help.
The trouble with this statement "seems. like a rule a bcc or a server configuration" is that it is inconsistent. It will happen on specific emails and at what seems to be random times.. Sometimes quitting mail and reopening will resolve but not always.
Also, just to follow up and make sure that I have been clear. We admin our own servers and we have not only checked our servers for rules, we have spun up Outlook accounts (this is on an exchange server), checked the rules in there; nothing. We checked Airmail for rules, nothing. We then used Outlook and the Outlook Web to forward two particular emails that I could not forward to another person in my office, on the same domain. Both worked.. Also, a detail that is very specific for me.. It always and only happens with one particular recipient that I forward to constantly.. Her email is, again, on the same domain and it may just be that the volume of mail I send to her is soo high that I only notice it when forward to her but as of this moment it has not happened when forwarding to anyone else.
Also, I have reported this before, I looked but could not find the thread that I posted on but it was a similar complaint.. I am not using Beta I have the latest paid for version.