Added FAQ

FAQ.md

@@ -134,6 +134,7 @@ FairEmail follows all the best practices for an email client as decribed in [thi
 * [(70) When will messages be auto expanded?](#user-content-faq70)
 * [(71) How do I use filter rules?](#user-content-faq71)
 * [(72) What are primary accounts/identities?](#user-content-faq72)
+* [(73) Is moving messages across accounts safe/efficient?](#user-content-faq73)
 
 [I have another question.](#support)
 
@@ -1147,6 +1148,17 @@ There can be just one primary account and there can be just one primary identity
 
 <br />
 
+<a name="faq73"></a>
+**(73) Is moving messages across accounts safe/efficient?**
+
+Moving messages across accounts is safe because the raw, original messages will be downloaded and moved
+and because the source messages will be deleted only after the target messages have been added
+
+Batch moving messages across accounts is efficient if both the source folder and target folder are set to synchronize,
+else FairEmail needs to connect to the folder(s) for each message.
+
+<br />
+
 ## Support
 
 If you have another question, want to request a feature or report a bug, you can use [this forum](https://forum.xda-developers.com/android/apps-games/source-email-t3824168).