I have not used the LDAP support much in FastMail recently. In the past, with a customer who used the LDAP support from the beginning, I had issues where the Base DN changed without notice (I think because FastMail dropped some legacy support they did not realize was still needed). Setting it up again according to the latest documentation worked. My suggestion would be to
- double check the App password and its options in FastMail;
- carefully check your setup against the LDAP section in https://www.fastmail.com/help/techni...sandports.html to ensure things like Base DN are still as before;
- if it still does not work, open a support ticket.