Many mail clients do not show the receiver of the mail, only the sender, in the inbox.
When a Group-Mail is received, it should be easy to see, that the mail is send to the group, not ony as a personal mail.
The response to the mail may very often be a choice of responding to sender, or responding to all in the group,but if it is not clear, that the original mail is send to the group, then response will too easily by to the sender only, without hte choice...
Solution: Most (all?) other solutions have the option to let the mailgroup add text in front of the subject, for new mails.
for example possibility to add "[groupname] " in front of the email, where [groupname] is jsut my example, and should be free text.
This way it will be easy to see how the mail is send, - and actually also very easy to filter/search.
Of course the pharase should only be added to first mail, so replies don't add [pharse ] again and again, in a conversation.