If you reply to an email the "original" email address will only be used by Thunderbird if there is an identity that matches that email address for that account. If such an identity is not available the default identity for that account is taken, if you hit Reply.
What you need to do is add extra identities to each of the accounts for the alternate email addresses.
However if you move a mail to [email protected] to the account for [email protected] and in the settings for that latter account add an identity with at "Your Name" specified with your name, and "Email Address" set to [email protected], then Thunderbird will put [email protected] as the return address if you press Reply (even if this is not the default).
You can add additional identities to an account by right clicking the account in Thunderbird's left pane, then clicking Settings, then on the Account Settings form that pops up click Manage Identities... (just above Ok in the lower right corner.
Click Add, and fill out the first two fields as described, and check that the appropriate SMTP server is selected (if you sent as [email protected] you might want to use the smtp server associated with that account and not the one associated with the account you add this extra identity to).
You need to do this on each account for all your email addresses (assuming you don't want to worry about where you move which mail) that you want to have their incoming email address as reply to address.
If you have 4 email accounts set up in Thunderbird, this requires you to add the3 "other" addresses as extra identities to each of the accounts, and for each select the appropriate SMTP server.
The above will result in no difference for the recipient (in headers, route etc) of a reply whether you first move an email from one account to another, or directly reply from the account where you received the email.
