Email not downloading properly

[#1]

I have just upgraded broadband and installed the new PlusNet router. Since then my wife's Hotmail emails are not downloading properly on her iPhone. I am not having any problems with my Android phone and my son is not having any problems with his iPhone. My wife doesn't have any problems when on 4G or wi-fi networks elsewhere.
I am baffled. Does anybody have any ideas?
Thanks.

[#2]

As two out of the three phones are not having problems, that points to  an issue with your wife's phone, not the connection.

Try, on the affected device, 'forgetting' your home connection, and then recreating it. If that doesn't work, try totally shutting the phone off, give it a couple of minutes and restarting it. Which iOS version is it on?