I have '''Thunderbird Mac 78.14.0 (64-Bit)''' on ElCapitan Mac OSX 10.11 I use GMX as email provider. (Germany) I have 3 accounts/emails using in Thunderbird. For example: "myname@gmx.de", "companyname@gmx.de", "private2@gmx.de") "companyname@gmx.de" is set as standard Identity. One of my 3 accounts has a '''second Alias-Identity''' "companyname@gmx.de" -> "name@myowncompany.com" Within these 2 IDs "name@myowncompany.com" is set as Standard ID With this alias ID I mail to all important customers, because its my companies name. As example: I write with "name@myowncompany.com" to "mister@BEN" So when "mister@BEN" replies to me on to "name@myowncompany.com" and I press in this mail "reply", Thunderbird will choose "myname@gmx.de"(??) as the "from" for my reply-mail to "mister@BEN" Why??? I could understand, if Thunderbird would choose "companyname@gmx.de" since it is affiliatet to the Alias "name@myowncompany.com", but why even from the complete wrong account "myname@gmx.de" that has no Alias ID at all? This Mailprogram is way too stressing with unwanted features. Thank You for Your help!