Admittedly I haven’t used gmail for years now but from what I remember when I used to do this this is half right. If you change the From address in gmail, it will add a ‘Sender:’ header with your gmail account on it. Some clients will show that combination as the email being from ‘X on behalf of Y’ where Y is the from address and X the sender address and some will send replies, especially bounces, to your sender address. It may also set off some spam traps. I think it might also have required some form of verification that you have access to the address in question.

If you want to send from a different address without the sender header being set to your gmail account, I think you have to have Gsuite.

I just looked at the headers from some emails I sent this way. My gmail address does not appear there and both the <From> and Return-path are my domain address.

Thanks. Looks like they fixed this quite a while ago and now either you can verify an account after which it will accept your From header (and the web and app UIs let you select that) or, if you haven’t verified the address then if you send an email through their SMTP servers it will rewrite the From as your gmail address and sets a new X-Google-Original-From header to the address you put in the email originally.

I just tested it and it does work from the Android Gmail app.

How? I just checked and couldn't find it.

You have to have added the other email addresses from your Gmail web page first, under Settings, Accounts and Import, Send Mail As. It will ask you for the server address and credentials etc.

Then when you compose a message from either the website or the Android app, your From address is a dropdown containing the addresses you set up.

https://support.google.com/mail/answer/22370?hl=en