Using sendmail with gmail
 

I tried to relay an e-mail through gmail June 1. gmail responds:
which doesn't help. The Username and Password are correct: I can log in with them on my browser.

Has anyone made this work?

As far as I know google has turned off use less secure apps for most users as of 30 May. Here is is a workaround.

https://wiki.archlinux.org/title/msmtp

I have mutt working with oauth2...

This might help, https://support.google.com/accounts/answer/6010255

As best as I can tell, Google requires either 2-factor authentication (all of which require a telephone number, which I lack) or an authentication key, which they sell for $30. Instead I made an old account elsewhere work and gave up on gmail.

I've never given them a phone number or paid a fee.
I simply went to the settings for the account directly on their site and confirmed they were correct.

Do you relay outgoing SMTP traffic through your account?

Yes.
I use Thunderbird to retrieve e-mail from their server and to send e-mail.
In Thunderbird, under outgoing server (smtp) settings,
it is,
description = whatever name you use
server name = smtp.gmail.com
port = 465
user name = your gmail account user name
authorization method = OAuth2
connection security = SSL/TLS

Google's use of 2FA breaks lots of programs, but they do have an option to make an App Password for that app.
Use the link in post #3, scroll down to the bottom to get info on setting one up. I used it to send a monthly email from one of may gmail accounts when the old company email stopped working when it was sold and the new company helpless desk could not help.

I tried that before I asked the question. The option to create an app password isn't there. They tell me that I need to use 2FA to create an app password. When I try to set up 2FA it requires: a phone, or phone number to send a text message or call to, or a security key. How do you get away without this?