Home mail server - inbound port 25 now being blocked?

[#1]

Hi,
I've been running my own mailserver at home for years with no problem. Today all the incoming mail is falling back to the failover server I have on the DNS configuration, (I use the plusnet mail server as fallback), and nothing is getting through on port 25 to my own mailserver.
I've checked manual connections to port 25 externally and there's no response.
Inside my home network the mail server works fine. It's also able to send out mail and the IMAP server is working fine, both internal and external.
I've checked the router (Technicolor 582n as supplied by plusnet) and it's still showing a port forward on port 25 to my server.
I'm on a static IP and double checked my MX records and they're correct. A blacklist check also shows no issues against my IP.
Is there a chance SMTP is now being blocked?  Up to now, PlusNet have been fine with running mail servers.
Cheers,
Tim.

[#2]

Has the PN firewall turned itself on perhaps?
https://portal.plus.net/my.html?action=firewall

[#3]

Hmm, you might be on to something there.
Just checked and it's set to 'low'. I've never enabled it myself.
I've set it to 'off' now, but can't check until I can reboot the router it seems so will have to wait until at home. I see there are advanced settings also to block common ports below 1024 but leave specifics open like SMTP, HTTP & HTTPS in case you're running those servers.
I wonder if the firewall has been turned on randomly or is this a new policy.

[#4]

Update - yes, that was the issue. It was blocking my web server also. Turned off PN firewall, stop and start broadband connection, all fine.
Cheers