I just upgraded to 0.54 and it appears that port 465 is blocked on IPV6. I’ve opened a ticket with Linode. For some reason it is saying that SMTP/postfix is not running on ports 25 or 587. Is this because of the port 465 problem or something else?
Unless you have changed the ufw settings, this is usually a problem with the provider (Linode, in your case). If they report they are not blocking any ports or only one port, it could possibly be a bug.