change sender address on the fly when composing new mail

I’m using my own domain for sending emails. Due to multiple reasons I’m using different email adresses for different recipients. So I’d like to be able edit the email address (the part before the  @-sign) when composing/replying to an email. That’s the one feature from Thunderbird I’m missing from eM Client. There I could select “user defined email address” from the drop down list with possible sender addresses, and then enter an individual address by hand.
If this isn’t possible right now, could this be added as a feature?

That is not possible in eM Client.

You can only use the address that is setup in the email account, or one of the aliases that you have assigned in the account settings.