George_B immediately spot one problem in my task... first requirement is too subjective. After I think about this, I get my believes. If I'm wrong, let someone correct me.
I just imagine.
If mail hosting service have 2500 users. And each receive two mails per month. For ten months... If each mail have 20MB attachment... all that will consume 1TB HDD space. One very small company will need to buy new HDD each year.
In same time, if on average one of 2500 users do 40 impressions per month... 10 months yield one million impressions. But after there are only 2500 customers... One advertiser will no need to pay more of 10€ ...
(no need to inform for your product someone already informed)
2500 users, only 2% are rich. We get 50 rich users. 10% of them advertise products... We just paid the HDD... but we haven't money to pay the electricity for the server.
I conclude... competitive email hosting is very expensive thing and advertisement can not pay it. The host company, to can survive... It need some kind of side business. And after we evaluate the effectiveness of this side business... We can more well imagine and be more objective about the assumption whether the company will survive after one year, after five years, after ten years hosting of free email accounts.
The company can have the wish to host you forever... but if it do not survive?
What are the side businesses of free email account providers?
() ISP (related to receiver of Internet stuff)
() webhosting (related to giver of Internet stuff)
() social network (related to the network of people's Internet stuffs)
() search engine (related to the need to receive information about other things)
() news agency (related to the need to provide information about other things)
Am I miss some profitable side business?
What to pay free email hosting?
Basically email business idea was good before years... It create network of people... and in each email account, people have database with contacts. This evolve to modern social networks like Facebook, where each profile have database with friends
Example for network of information about other things can be wikipedia. But they are so about other things, they're so far of closely related to Internet like IMAPS.
Other example, out of subject... how one business is not profitable in developed countries, to understand more clear, what's going on with the world. In third world, there are popular these Internet computer labs with dozens computers. People go there and pay to use the PC. It's some kind of rental service. This kind of business in developed country is not profitable, because everyone have PC in home
Resume: After we evaluate the business strategy of company, we can predict them future.