Outlook 2013 cant connect to SMTP error 421 / 0x80042109 - fixed, but uh?

I noticed I had a problem with sending mail last week, which has just been fixed by my ISP (who are not my mail provider). I can see exactly what they've done, but it doesn't make sense...! Can someone help?

I first noticed the problem last week when sending mail via Outlook, where I was getting the error mentioned in the subject line - cannot connect to SMTP / error 421 / 0x8004219. I could still receive mail without a problem. I had made no changes to the set up at all (same setup I've had for years, through multiple ISP changes), but I have changed my ISP in the last month. I hadn't sent any mail since changing broadband provider until last week.

My Mail Provider settings are:

mail.freenetname.co.uk
smtpmail.freenetname.co.uk

Outgoing mail requires authentication

Incoming server - port 110
Outgoing server - port 25

I am still able to use these settings on my mobile, as long as I'm not using my home wireless / broadband to connect. If I use wireless, mail will not send.

I had run a repair on the PST file, and had played with settings in Avast - 2 potential solutions, which didn't make a difference, so I contacted my ISP today.

After a bit of investigation, she made a change to my outgoing mail server, which is now:

smtp.orangehome.co.uk
untick outgoing mail requires authentication

and now mail works. and I don't understand why! Surely my mail settings are governed by my mail provider, not my ISP? Otherwise they wouldn't still work on my phone?

Is my mail now being sent via Orange / EE, rather than via my mail provider??

Will my mail still work on my mobile phone if I change the outgoing server to Orange?

I'm confused!!!!!!

Can anyone help??