How to reply from the same email account?

Question

I have multiple email accounts. When I receive an email from an alternate account, not the default account, and I respond to this email it is automatically responding from the default account.
I can change it to an alternate email address as on previous iOS versions- that's not my question.  I just want to be able to reply directly from the account the email was sent to. Am I missing something?
* kudos to the multiple signatures one for each account, but it doesn't help if I'm responding from the wrong account.

Answer 1

I think there is a contradiction in your requirements. You want two people to share an account and you don't want either to interfere with the other.
The short and simple answer is to use IMAP to connect to the mail server. If your current email provider doesn't offer IMAP, find another that does. This is old technology already and it's disgraceful that some email providers haven't yet put it in place.
IMAP means that your messages are stored on the server and both of you will see exactly the same set of messages. And therein lies the contradiction; you will both see changes made by the other so you are inherently interfering with one another.
Caveats: some providers may not permit you both to access the account concurrently, and even if they do, things may become interesting if you both choose to work on the same message simultaneously.
Note that all of this is about email servers and protocols; your choice of Thunderbird as your email client has little bearing on the situation.