Updated FAQ

FAQ.md

@@ -1991,6 +1991,13 @@ Since the app needs to wait for responses of the email server, which requires th
 If you are comparing the battery usage of FairEmail with another email client, please make sure the other email client is set up similarly.
 For example, comparing always sync (push messages) and (infrequent) periodic checking for new messages is not a fair comparison.
 
+If you are comparing the battery usage of FairEmail with an app like Whatsapp,
+please understand that most apps use [Firebase Cloud Messaging](https://firebase.google.com/docs/cloud-messaging) (FCM) for push messages,
+which means that no battery usage will be contributed to an app for push messages, but instead to the Google Play Services system component.
+Apart from the privacy concerns, it is not possible to use FCM for email because email servers do not support FCM.
+The only way would be to download all your messages to a third-party server first and use FCM to push notifications to the app.
+The privacy and security implications would be significant, though.
+
 Reconnecting to an email server will use extra battery power, so an unstable internet connection will result in extra battery usage.
 Also, some email servers prematurely terminate idle connections, while [the standard](https://tools.ietf.org/html/rfc2177) says that an idle connection should be kept open for 29 minutes.
 In these cases you might want to synchronize periodically, for example each hour, instead of continuously.

index.html

@@ -1116,6 +1116,7 @@ X-Google-Original-From: Somebody &lt;somebody+extra@example.org&gt;</code></pre>
 <p>As a rule of thumb, the battery usage should be below or in any case not be much higher than <em>Mobile network standby</em> for one account with a stable network connection. If this isn’t the case, please turn on <em>Auto optimize</em> in the receive settings tab page. If this doesn’t help, please <a href="https://contact.faircode.eu/?product=fairemailsupport">ask for support</a>.</p>
 <p>It is inevitable that synchronizing messages will use battery power because it requires network access and accessing the messages’ database. Since the app needs to wait for responses of the email server, which requires the processor (CPU) to be active, slower email servers will result in more battery usage.</p>
 <p>If you are comparing the battery usage of FairEmail with another email client, please make sure the other email client is set up similarly. For example, comparing always sync (push messages) and (infrequent) periodic checking for new messages is not a fair comparison.</p>
+<p>If you are comparing the battery usage of FairEmail with an app like Whatsapp, please understand that most apps use <a href="https://firebase.google.com/docs/cloud-messaging">Firebase Cloud Messaging</a> (FCM) for push messages, which means that no battery usage will be contributed to an app for push messages, but instead to the Google Play Services system component. Apart from the privacy concerns, it is not possible to use FCM for email because email servers do not support FCM. The only way would be to download all your messages to a third-party server first and use FCM to push notifications to the app. The privacy and security implications would be significant, though.</p>
 <p>Reconnecting to an email server will use extra battery power, so an unstable internet connection will result in extra battery usage. Also, some email servers prematurely terminate idle connections, while <a href="https://tools.ietf.org/html/rfc2177">the standard</a> says that an idle connection should be kept open for 29 minutes. In these cases you might want to synchronize periodically, for example each hour, instead of continuously. Note that polling frequently (more than every 30-60 minutes) will likely use more battery power than synchronizing always because connecting to the server and comparing the local and remote messages are expensive operations.</p>
 <p>If you know that the connection (reception) is bad, it might be worthwhile to decrease the timeout value in the connection-settings tab page to 10–20 seconds, so that the app discovers earlier that no connection is possible, so that the mechanism as described in <a href="#faq123">this FAQ</a> is used faster.</p>
 <p><a href="https://dontkillmyapp.com/">On some devices</a> it is necessary to <em>disable</em> battery optimizations (setup step 3) to keep connections to email servers open. In fact, leaving battery optimizations enabled can result in extra battery usage for all devices, even though this sounds contradictory!</p>