Accessing website knocks out our email?

Hi,

So I recently set up my architects office with a new website with zero issues whatsoever.

I then left the office to return to college and they have been experiencing technical difficulties when accessing the website, which have progressively gotten worse.

It’s now at the stage where they can not log in to the website to make any changes and when they attempt to do so their email goes down. Their email and their website are hosted on the same network. May be worth noting that the website does not ever go offline during this, only the email.

Is this a known issue? If not how can I get around it?

Thanks for your help!

The page I need help with: [log in to see the link]