How does the Inactive state work?
When your account is set to Inactive Postcrossing will not select your account to receive postcards. However, when you set it back to Active you will receive all postcards that your account should had received during that time.
If you know you are going to be away for some time (for example: on holiday, a business trip, etc.), you can set your account to Inactive. You can do that at any time in your edit account section and also you can restore it to Active whenever you want.
It is a good idea to use this option whenever you are going to be away from your address for more than a week so that other members do not send you postcards that you are unable to register. It is also advisable to set your account to inactive in advance of your departure so that you can register all postcards that are still traveling to you.
If you plan to return after a short period of time (example: vacation) and you wish to continue sending postcards while on Inactive status, you can. Note however, that if the period of inactivity is too long, the Postcrossing system might temporary block you from sending more postcards if the difference between sent and received postcards is too large for your account. However, this block will automatically go away once you reduce the difference between sent and received postcards. To do that, simply set your account back to active and register the due postcards as soon as they arrive to you.