Based on what you said is blocked I think email is out of the picture. Is there a reason you can not call them on the phone and/or use voice calls to set up Zoom calls?
I want a trial of mail that can be shared with others, rather than call recordings and video recordings, that can't be shared that easily and would be far greater in size.
If the lawyers are not using the domain of their law firm are you sure you are dealing with real lawyers and not scammers? If it is the domain of their lawfirm then you should be able to get contact information off their website. Something is off about all of this.
No, I mean I'm using a email service on top of my own domain, and the people I want to contact only have their email ids listed online and I want to have contact via email prior to having a voice call or video call for which I need a two way communication via email.