Enter 2 email addresses for a contact

I completely agree with the users’ comments. I have just switched over from Insightly, am now paying £500 + per month and the one email address to one contact is a major issue.
To an extent, I could live with it short-term if there was a way to manually link a received email to more than 1 contact when forwarding from Gmail (same an Insightly does), but there isn’t. So emails get split over several ‘same’ contacts & we completely lose the thread of the conversation.
This is basic stuff for a CRM system.
Thanks
Andy