Firefly III breaks when installing - Sender address rejected: not logged in

[systeminfo]

Yunohost Version 11.1.21.4.
Fresh install of Firefly III.

After successfully launching, it prompts me to register an account. I put in an email and password, and after a good 30 seconds loading it gives me:

FireflyIII
Whoops! An error occurred.
Unfortunately, this error was not recoverable :(. Firefly III broke. The error is:

Expected response code "250/251/252" but got code "553", with message "553 5.7.1 <myusername@domainhidden>: Sender address rejected: not logged in".

This error occurred in file /var/www/firefly-iii/app/Jobs/MailError.php on line 103 with code 0.

More information
Please collect more information in the storage/logs directory where you will find log files. If you're running Docker, use docker logs -f [container]. You can read more about collecting error information in the FAQ.

Get help on GitHub
You're more than welcome to open a new issue on GitHub.

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Include the information from this debug page.
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Include error logs (see above).
Tell us what you were doing.

Additional info

Github issue: FireflyIII breaks when installing - Sender address rejected: not logged in · firefly-iii · Discussion #7693 · GitHub
ff3-fcgi logs: debian Pastezone
ff3-cli logs: debian Pastezone
ff3-audit logs (personal data removed):

[2023-06-27T10:43:14.923311-04:00] local.INFO: AUDIT: Show login form (1.1). (my.ip.address -> GET:https://yunohost.mydomain.com/firefly/login) [] []
[2023-06-27T10:43:19.935712-04:00] local.INFO: AUDIT: Show login form (1.1). (my.ip.address -> GET:https://yunohost.mydomain.com/firefly/login) [] []
[2023-06-27T10:50:50.763454-04:00] local.INFO: AUDIT: Show login form (1.1). (my.ip.address -> GET:https://yunohost.mydomain.com/firefly/login) [] []
[2023-06-27T10:51:01.283860-04:00] local.INFO: AUDIT: User is trying to login using "sig_firefly@mydomain.com" (my.ip.address -> POST:https://yunohost.mydomain.com/firefly/login) [] []
[2023-06-27T10:51:01.356303-04:00] local.INFO: AUDIT: User "sig_firefly@mydomain.com" has been logged in. (my.ip.address (sig_firefly@mydomain.com) -> POST:https://yunohost.mydomain.com/firefly/login) [] []
[2023-06-27T10:53:55.496804-04:00] local.INFO: AUDIT: Show login form (1.1). (my.ip.address -> GET:https://yunohost.mydomain.com/firefly/login) [] []

[toastface]

I also had this issue. After some digging around I found out that there are settings stored in a file called .env in the firefly-iii folder. In my installation this was in /var/www/firefly-iii. Scroll down until you find the mail settings. I had to add in the username and password from my yunohost account (name and password)

MAIL_MAILER=smtp
MAIL_HOST=127.0.0.1
MAIL_PORT=25
MAIL_FROM=name@*************
MAIL_USERNAME=name
MAIL_PASSWORD=password
MAIL_ENCRYPTION=null

This got it working for me.