The server owner of the mail server your message was sent to has opted to utilize this block list. This block list will block all mail sent from any domain that was registered less than 5 days ago. Once your domain name has aged beyond 5 days from its original registration date, it will be automatically delisted from this block list and you should be able to send mail to servers using this block list without any trouble.
Frustratingly, a relatively new tactic used by mass spammers is to register thousands of cheap brand new domains. Once they do this, they blast out large amounts of spam from them. Since the domains are so new (usually only a few hours old), most anti-spam block lists haven't had a chance to evaluate their behavior and list them as bad domains. This list targets this type of spam by blocking all mail from any domains that are less than 5 days old from their original registration date. The belief being that legitimate users will continue to use their domains after 5 days, whereas spammers will end up abandoning their domains within the first day or two because other block lists will have marked them as spammers. I agree that this does mean frustration for new site builders, but the hope is the first few days will be spent setting up your website and that your domain will be off this blocklist before you actually start to make use of it.
This block list does not accept delist/removal requests. This is because any domain blocked by this list will be automatically unblocked within a maximum of 5 days. For example, if your domain was registered on 2015-04-10, and you sent email on 2015-04-12, it would be blocked by this list for being less than 5 days old. However, upon 2015-04-16 (5 days after 2015-04-10), your domain will automatically be removed from this list.
We attempt to make sure that the window of time that domains are blocked are precisely 5 days from their registration date (right down to the second). However, this is not always possible since some registrars do not publish precise dates that include hours/minutes and sometimes they do not publish the time zone of the registration date. As a result, it is possible that the actual block time of a domain may be as few as 4 days or as long as 6 days. This variance is by design as to make sure that a block, regardless of how precise or not the published registration date, would never last more than one week. In most cases, however, the block duration would be up to 5 days.
No. The only date we block based off of is the initial registration date of a domain. We do not look at renewal dates, expiration dates, or any other dates. Even when you tranfser between registrars, the original registation date is kept with your domain. The only case where a domain could be "re-blocked" is if it is left to expire entirely from a domain registry and then re-registered brand new again.