What is the email attachment limit using Plusnet as carrier, not PN emails

[#1]

I use a separate web-based ISP for all my emails.
I don't use PlusNet email.

I used to be able to send emails, using PlusNet Broadband, with attachments up to 100mb.
These now get rejected, no warning, they just don't get through.
I use Apple Mail POP3 for my emails.
The new limit seems to be about 30mb per email, can anyone confirm what the actual limit is nowadays.
Whichever of my other three web-based email ISP's I send to, the limit is there, so the limitation has to be in the PlusNet system.
I have always received a notification that my email is over 100mb limit, on every OTL email, previously, sent through Plusnet ... see screen grab below.
Today I get one notification if I am lucky, out of a batch of 15 with attachments size over 30mb I send.
And it doesn't specify a limit.
This is sending emails from Apple Mail to other web based ISP emails, I'll try it in reverse and see what happens, so it doesn't originate through my PlusNet broadband, and see what error messages I get

[#2]

$ telnet relay.plus.net 25
Trying 212.159.8.107...
Connected to relay.plus.net.
Escape character is '^]'.
220 avasout08 smtp relay.plus.net
ehlo test
250-avasout08 hello [84.92.153.186], pleased to meet you
250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 104857600
250-PIPELINING
250-8BITMIME
250 OK

250-SIZE 104857600 suggests it's not the Plusnet SMTP server(s) imposing the limit you've come up against.