No. You need the username, password, protocol, port number, and address for the server. The size of the organization has nothing to do with whether you can access it or not. You'll definitely need to ask the user for their username, password, and who the mall provider is. You can probably just have a database with the protocols, port numbers, and addresses of the most common mail providers (gmail, iCloud, yahoo, etc).
If you go into Settings > Mail > (pick a mail account) and dig around, you can find all of the above info... At least for some account types. I couldn't find the info for my iCloud account. Apple probably just hard coded the port number and address and protocol so that you can't break the account by changing those settings.