Added FAQ

FAQ.md

@@ -164,6 +164,7 @@ FairEmail follows all the best practices for an email client as decribed in [thi
 * [(94) What does the red/orange stripe at the end of the header mean?](#user-content-faq94)
 * [(95) Why are not all apps shown when selecting an attachment or image?](#user-content-faq95)
 * [(96) Where can I find the IMAP and SMTP settings?](#user-content-faq96)
+* [(97) What is 'cleanup' ?](#user-content-faq97)
 
 [I have another question.](#support)
 
@@ -1568,6 +1569,24 @@ The IMAP settings are part of the (custom) account settings and the SMTP setting
 
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+<a name="faq97"></a>
+**(97) What is 'cleanup' ?**
+
+About each four hours FairEmail runs a cleanup job that:
+
+* Removes old message texts
+* Removes old attachment files
+* Removes old image files
+* Removes old local contacts
+* Removes old log entries
+* Updates contact photos of messages
+
+You can see when the last cleanup was performed at the bottom of the advanced options.
+
+Note that the cleanup job will only run when the synchronize service is active.
+
+<br />
+
 
 ## Support