Updated FAQ

FAQ.md

@@ -42,6 +42,7 @@ For authorizing:
 * Yahoo, AOL and Sky, see [question 88](#user-content-faq88)
 * Apple iCloud, see [question 148](#user-content-faq148)
 * Free.fr, see [question 157](#user-content-faq157)
+* Posteo: please check if [additional email account protection](https://posteo.de/en/help/activating-additional-email-account-protection) isn't enabled
 
 Please see [here](#user-content-faq22) for common error messages and solutions.
 
@@ -1089,6 +1090,12 @@ Sometimes it is necessary to enable external access (IMAP/SMTP) on the website o
 Other possible causes are that the account is blocked or that logging in has been administratively restricted in some way,
 for example by allowing to login from certain networks / IP addresses only.
 
+* **Free.fr**: please see [this FAQ](#user-content-faq157)
+* **Gmail / G suite**: please see [this FAQ](#user-content-faq6)
+* **iCloud**: please see [this FAQ](#user-content-faq148)
+* **Posteo**: please check if [additional email account protection](https://posteo.de/en/help/activating-additional-email-account-protection) isn't enabled.
+* **Yahoo, AOL and Sky**: please see [this FAQ](#user-content-faq88)
+
 If needed, you can update a password in the account settings:
 navigation menu (left side menu), tap *Settings*, tap *Manual setup*, tap *Accounts* and tap on the account.
 Changing the account password will in most cases automatically change the password of related identities too.