Most free email providers are not actually free - they are either partly or wholly supported by advertising. We're providing users the option of a free account with some simple ads to support these accounts, or for a small cost, can upgrade and remove the advertising entirely.
We are currently running a trial to investigate the effectiveness of some advertising on Guest accounts. If this trial is successful, we hope to be able to invest the revenue gained back into the company to improve our services and features.
We are using some graphic advertisements from third-party providers, but we won't ever be using popups or popunders, and we try to remove the most obnoxious ads.
We also structure our pages in such a way that the advertising should never slow down the speed of loading. Any external advertisement is loaded only after the rest of the page is displayed.
Currently, advertising is only displayed on Guest accounts active for more than one month. There are (at least) two reasons for this:
People who open a Guest account as a try-before-you-buy account, and then upgrade to one of the paid accounts within the first month, will never see advertising. This seems fair. It also means that they can see what the web interface is like without the advertisements getting in the way.
People who remain at Guest level indefinitely can maintain their account, but are presented with advertising to help defray the cost of providing the account.
Only free accounts have advertising displayed on them. All paid and upgraded accounts have no advertising. To upgrade your account, just click the Upgrade link at the top of any screen after you've logged into your account.