Tootfinder

Blocking outbound port 25 is fine these days (for dynamically numbered networks, like residential ISPs, etc).
(But port 465 shouldn't be described as "Legacy SMTPS", since 2018 it has been the recommended port for secure email submission - RFC8314 section-3.3.)

Broadband ISP YouFibre UK Set to Block Email Internet Port 25 from Friday
Internet service provider YouFibre, which is one of the main retail outlets for Netomnia's growing national Fibre-to-the-Premises (FTTP) based broadband network

Sigh: I've just asked my MP to ask the CMA to stop this; I jumped to Youfibre (that uses Netomnia) from Virgin as soon as possible.
https://www.ispreview.co.uk/index.php/2026/02/virgin-media-o2-uks-own…

Virgin Media O2 UK's Owners Close in on £2bn Broadband Deal for Netomnia
European telecoms giants Telefónica and Liberty Global, the joint owners of Virgin Media and O2 in the UK, have reportedly now joined with private equity firm

Now running IPv6 from my desktops - I'm using internal ULA addresses with masquerading, partly to spite IPv6 people, but mostly so in theory I can flip to a backup connection easily.
That does mean I've had to change /etc/gai.conf to label the ULA range ( fc00::/7 ) the same as generic routing - i.e. a label of 1
(It also assumes my ISPs - YouFibre - IPv6 routing holds together..it took 4 rounds with support to get them to fix it, and others have complained about IPv6 i…