I suppose that hosters who provides unlimited mail quota are only claiming it unlimited, and hope that they won't run out of disk space. Correct me if I'm wrong.
In order to do such trick they will have probably to calculate the average real quota used by the average user.
Let's say on a 100 GB space hosting I offer to 20 x 1GB POP3 emails, obviously if all user fill their mail my server would stop working cause they would require 200 GB, but I think I can expect this trick to work cause it will never happen (or it's extermly unprobable) that all user fills up all their mails, average user use Outlook and some will leave mail on server, others won't leave mail on server except when they are on vacation cause theyr PC is off and Outlook won't download mails.
But the QUESTTIONS are:
- What's the average email usage?
- Can we say that a user normally fills up 1/2 or 1/3 of the quota you provide him?
Thanks to any answers/suggetions you might provide.
It will depend entirely on the users and what they're using the e-mail accounts for. Your average soccer mom will have different needs than someone who is e-mailing 20MB CAD drawings all day long. Also, are they POPing mail out and removing it from the server, or are they using IMAP or webmail where the mail will stay stored on the server forever?
I can tell you on one of our mail servers, we're housing around 1,400 accounts for various small to medium-sized businesses. Some use IMAP and have several GB of storage, others POP mail out and hardly have more than a few MB on the server at any one time. It will really all depend on who the users are and what they're doing.
The other thing to keep in mind is that larger providers who offer "unlimited" storage have essentially "unlimited" money and other resources to throw at their storage platform. If they see that their storage is getting within a certain percentage free, they just add more and call it a day. If you're planning on offering "unlimited" storage with a 100GB drive, I'd highly recommend getting an idea of how your users will expect to use the service, and perhaps even put a quota in place that is higher than what you expect the majority of the users to consume, thereby protecting the system from the 20% who will want to use it as storage for their music archive or something.