2 accounts but replies only come from 1 account

V. 10.4.4209.
I have a Gmail account and a custom local account and it used to be that when someone emailed my Gmail, replies would come from that same address. I operate from All Inboxes and have never had a problem with this. Lately, though, all replies come from my custom account. I would like it to function like it used to, where replies came from the same address the original was sent to. Is there a new setting or workaround for that?
…OK, I just checked individual inboxes and the specific email I’m dealing with was most recently sent to my Gmail but doesn’t show up in my Gmail inbox at all, but rather my custom inbox. There are a couple replies in the thread from my custom account but most of the correspondence is to/from my Gmail. I would expect the most recent Sent To address to be the indicator of which Inbox to find that email.

V10.4.4209.
I have a Gmail account and a custom local account and it used to be that when someone emailed my Gmail, replies would come from that same address.

I operate from All Inboxes and have never had a problem with this.

If I reply to senders who email my Gmail address using All Inboxes & V10.4.4209, after it sends it has my Gmail address as the sender and replies still come from their email address back to my Gmail address exactly the same as previously.

Make sure you have your Gmail address “set as the default” and not your Local Mail account via “Menu / Accounts” which might be why it’s happening possibly defaulting to the wrong one.

OK, I just checked individual inboxes and the specific email I’m dealing with was most recently sent to my Gmail but doesn’t show up in my Gmail inbox at all, but rather my custom inbox

You may possibly have a eg: Custom rule setup to automatically move specific email senders arriving in your Inbox to your custom Inbox. So go to “Menu / Rules” to check. You can dblclick rules in there to view them apart from the default POP Spam rule.