There's an add-on called Cardbook which provides an alternative address book for Thunderbird. I can't work out how many email accounts it allows per contact but it might be worth trying?

https://freeshell.de/~kaosmos/morecols-en.html

The Cardbook add-on sounds great, except that it is an add-on.

Thunderbird really needs a feature for adding new fields in contacts, not just for additional email addresses.

Thunderbird is designed as open source so I doubt they change that just for you.

Airmail said

Thunderbird is designed as open source so I doubt they change that just for you.

Why would you suggest it was just for me? I am not so petty.

You can find the ability to add new fields in contacts all over the place. Just look at most cell phones. It is a real feature that makes sense.

And you were suggested 2 add ons to do just that. The More Functions for Address Book does that and more.

There are just as many people here complaining that Thunderbird does too much as people like you claiming too little. That is what add ons are for.