If you use Gmail it is easy to add Emails to send from without any additional services. The only thing is you need to have 2FA enabled. Without 2 factor authentication you will not be able to follow the next steps, specifically adding a application password, which is needed for this kind of configuration.
Keep in mind that this is undocumented and a relict of a old function google provided. It can happen that at some point Google will disable this functionality. This said, it works for us for over 5 years now.
If you use Inbox over Gmail you need to go to the Gmail interface in order to make this working. This is not a issue and will work back with Inbox as well, Inbox just does not seem to have the configuration interface needed.
smtp.gmail.com, port is right already.
Now you can choose which email to send from when you compose a new mail. It will also automatically use the right email when you respond to a mail.