Sending E-Mails from an iCloud Custom Domain, in case anyone else wants to

[OddMagnet]

Hey!

I was trying to send an email from my domain via iCloud custom domain and stumbled upon some problems.
Couldn't really find a solution by googling, so I thought I'd post it here so others can find it.
Feel free to ask questions or add more information if you think it'd be helpful for others.

I used the docker compose exec worker ak test_email [email protected] command for testing
The values I used are from here: https://support.apple.com/en-us/102525
This is how the environment variables in my compose file look (attached to the worker container):

      # E-Mail Config
      # SMTP Host Emails are sent to
      - AUTHENTIK_EMAIL__PORT=587
      - AUTHENTIK_EMAIL__HOST=smtp.mail.me.com
      # Optionally authenticate (don't add quotation marks to your password)
      - [email protected]
      - AUTHENTIK_EMAIL__PASSWORD=app-specific-password-generated-in-icloud
      # Use StartTLS
      - AUTHENTIK_EMAIL__USE_TLS=true
      # Use SSL
      - AUTHENTIK_EMAIL__USE_SSL=false
      - AUTHENTIK_EMAIL__TIMEOUT=10
      # Email address authentik will send from, should have a correct @domain
      - [email protected]

However, here I got the following error:
smtplib.SMTPAuthenticationError: (535, b'5.7.8 Error: authentication failed')
The app specific password was correct, since I copied and pasted it.

I then tried using my apple-id for the AUTHENTIK_EMAIL__USERNAME, but then I get this error:
smtplib.SMTPAuthenticationError: (550, b'5.1.1 Mailbox does not exist')

The Solution
Since my Apple-ID was an @googlemail.com address neither the full address ([email protected]) nor just the name (my-name) worked.
I remembered that I had 2 aliases for my primary mail:
[email protected] and [email protected]
Simply using first-name.last-name for AUTHENTIK_EMAIL__USERNAME worked for me.

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Hope this helps someone else in the future :)