In theory you could have as many broadband email accounts as you like. It simply depends on how many providers you use in your lifetime and whether you set set an email account up with them at the time. The issue is keeping track of them all.
As we've mentioned earlier in this article, when you switch between providers some of your email accounts will be turned off, or they'll cost you money to keep them going. So if you have several of these, without properly managing them you could lose important information or end up having to spend significant amounts to keep using them all.