External FTPS server connection issue

[steveTu]

Filezilla Client 3.62.2

I am trying to replace Netgear's Readycloud with a simple FTP(S) connection. Netgear's ReadyNAS offers an FTSP server via proftpd. The service is FTPS.
I have configured the server and have tried to connect to the server via my phone (using Files+ and AndFTP) and also from my laptop (using Filezilla). The phone connects to the NAS's WAN address perfectly ok from both apps. Filezilla starts to connect, but then gets a connection timeout. I can connect from Filezilla to the local LAN address perfectly ok though.
I have just tried to connect to another remote FTPS server ( ftps.cs.brown.edu) and get the same timeout.

The connection display shows:
09:05:38 Status: Resolving address of xxxxxx.ddns.net
09:05:38 Status: Connecting to xx.xxx.xxx.xx:21...
09:05:58 Error: Connection timed out after 20 seconds of inactivity
09:05:58 Error: Could not connect to server
09:05:58 Status: Waiting to retry...
09:06:03 Status: Resolving address of tucknotts.ddns.net
09:06:03 Status: Connecting to xx.xxx.xxx.xx:21...
09:06:23 Error: Connection timed out after 20 seconds of inactivity
09:06:23 Error: Could not connect to server
09:06:25 Status: Disconnected from server
09:06:25 Status: Resolving address of ftps.cs.brown.edu
09:06:26 Status: Connecting to 128.148.32.15:21...
09:06:46 Error: Connection timed out after 20 seconds of inactivity
09:06:46 Error: Could not connect to server
09:06:46 Status: Waiting to retry...
09:06:51 Status: Resolving address of ftps.cs.brown.edu
09:06:51 Status: Connecting to 128.148.32.15:21...
09:07:11 Error: Connection timed out after 20 seconds of inactivity
09:07:11 Error: Could not connect to server

...any ideas as to why? My router would appear to be configured ok, as my phone's apps connect ok. The ReadyNAS seems to be be configured ok as I can connect remotely (via phone) and locally (all devices). Filezilla appears to be configured ok (for local connections anyway!).

[botg]

Either there is no working server at that address, or FileZilla is being blocked by some firewall.

[steveTu]

The server is running - the phone connects perfectly ok and goes through the same router/firewall as my laptop.
If I move my laptop to a remote location (outside of my LAN) I still cannot connect from Filezilla on my laptop - but still can connect perfectly ok from my phone.
I can connect from Filezilla to the local address from within my LAN perfectly ok.

So I know the FTP server (proftpd) is running and working. I can get through the firewall on my router via my phone's apps. Proftp is configured for FTPS/FTPES and uses TLS 1.2 max, may laptop uses TSL1.3 - are there any known issues with connecting to an FTPS server running 1.2?

[botg]

There's gotta be some firewall involved.

[steveTu]

Would I be right to assume that the firewall must be then outbound on my laptop? As the phone (which presumably still must come through my inbound router/firewall) works fine.

[botg]

Sounds reasonable.