I have just received the following somewhat cryptic message from the company that hosts my server:
We have checked further
The port is not blocked, inside the server
[root@operations ~]# telnet smtp.fastmail.com 465
Connected to smtp.fastmail.com.
Escape character is '^]'.
I have sent a further urgent message to them to ask for more details clarifications and before they disappear on me again, but send you this in the mean time.
I will be back with more info as and when