diff --git a/FAQ.md b/FAQ.md
index 7c1bc55d3e..79bb30483f 100644
--- a/FAQ.md
+++ b/FAQ.md
@@ -1050,6 +1050,7 @@ Too large messages and triggering the spam filter of an email server are the mos
 * The attachment size limit for Outlook and Office 365 [is 20 MB](https://support.microsoft.com/en-us/help/2813269/attachment-size-exceeds-the-allowable-limit-error-when-you-add-a-large)
 * The attachment size limit for Yahoo [is 25 MB](https://help.yahoo.com/kb/SLN5673.html)
 * *554 5.7.1 Service unavailable; Client host xxx.xxx.xxx.xxx blocked*, please [see here](https://docs.gandi.net/en/gandimail/faq/error_types/554_5_7_1_service_unavailable.html)
+* *501 Syntax error - line too long* is often caused by using a long Autocrypt header
 
 **Gmail errors**