When replying to an email that is sent to my alias address, Thunderbird uses my actual email address in the reply email unless I manually change it. This should be either automatically the same address the email was sent to or at least optionally selectable choice in preferences instead just always using my default email address. Longer version: 1) I order something from Acme Inc. I give them my alias email in format of user@acmeinc.domain.etc. 2) there is an issue with the order. Acme Inc contacts me by sending email to user@acmeinc.domain.etc 3) I get the email. I reply by pressing the reply option in Thunderbird 4) Thunderbird sets my sender address as user@domain.etc instead of using the email address user@acmeinc.domain.etc the email was sent to 5) Before sending the email I will have to manually go and type in the address that I want to use so that a) my actual email address is revealed to automatic systems b) I can potentially be able to see who leaked my email address and where (marketing, spam, ..) '''The format of the email address is not an issue. The email address used when replying is.''' Please make it so, that when pressing the reply button the same email address the message was sent to will be used by default, or atleast add this as an option for the user to select in the preferences. The fact that email programs have junk (e)mail options does not remove the fact that junk mail still happens and the actual solution is to remove unwanted junk at the server, not the client level (we have many, many, nice devices, don't we).