This article http://kb.mozillazine.org/Mozilla_Suite_:_FAQs_:_Mail_Aliases explains how Thunderbird handles multiple identities. I think it's saying that what you want to do is not the normal setting, but it includes a helpful summary of relevant add-ons. If you set up a filter so that mail received for 'address 2' is directed to its own folder, then I think the Folder Accounts add-on might do what you want?

Hi, thanks for your reply but I already read that article prior posting here. What is strange to me, is that the default behaviour seems not working for me. I have only one folder account, the other is only an identity used to send e-mail with a specific address.

The article says: 'When you reply to a message, Thunderbird uses the identity that matches the address the message was originally sent to' So if you receive a message sent to address 2, and you reply to it, you should see address 2 in the 'from:' field of your reply. That's the default behaviour. I assumed that a) that is exactly what you are seeing b) that is not what you want, since you say: 'when I receive an e-mail directed to address 2 and I click on reply, I would like that in from: field I have the address 1' I'm sorry if I have misunderstood you?

You understand perfectly :) So, do you think that Folder Accounts addon could solve my issue? I'll do a try, thanks

Solved with Folder Accounts add-on that adds the option that I was searching for in Folder Properties: "From Account" :) Thank you man!

Solved with Folder Accounts add-on that adds the option that I was searching for in Folder Properties: "From Account" :) Thank you man!