FairMail OIDC with self-hosted Dovecot

Took me some time to figure this out, too

Follow steps outlined in FairMail FAQ:

1. Open FairMail app Miscellaneous Settings,

2. Temporarily enable Debug Mode to display the debug panel.

3. Open the debug panel and click the button to import the XML file.

4. After importing the file, use the Quick Setup Wizard to configure an account.

XML file for step 3:

<?xml version="1.0" encoding="utf-8"?>
<providers>
  <provider name="Shpakovsky Mail" id="shpakovsky" domain="shpakovsky\.ru" order="1">
    <imap host="imap.shpakovsky.ru" port="993" starttls="false"/>
    <smtp host="smtp.shpakovsky.ru" port="465" starttls="false"/>
    <oauth enabled="true" askAccount="true" prompt="login"
        authorizationEndpoint="https://auth.shpakovsky.ru/authorize"
        tokenEndpoint="https://auth.shpakovsky.ru/api/oidc/token"
        clientId="..."
        clientSecret="***SECRET***"
        redirectUri="eu.faircode.email:/"
        scopes="openid email profile"/>
  </provider>
</providers>

Remember to paste actual client id and secret, that your OIDC provider (TinyAuth in my case) will recognize!

Also note that unlike Thunderbird, FairEmail requires OIDC login for both IMAP and SMTP servers. Luckily, dovecot supports exactly this - it offers a "submission" SMTP server with dovecot-provided OIDC login and forwards connections to another SMTP server, with login-password auth, for actual email delivery.