The Mailing System is a feature added of theupdate. It allows players to send mail to any player. It was deactivated on iRO for a time due to bugs, but returned to iRO when the update occurred. It was deactivated again because of a duping bug and reintroduced again later during the update.
You can send mail via your Friends list (as long as you have one friend), your Party list (as long as you are in a party), or through the Mailbox. Your mail is accessed via a Mailbox NPC in all major towns. There is a fee of 130 Zeny to access the mailbox. Mail will be deleted automatically once your mailbox is full, starting with the oldest messages. You can have a maximum of 30 messages at once. Any mail you have opened must be taken care of in order to see next one.
Zeny and Items (1 item stack per message) can be sent via the Mailing System. Character and account-bound items such as Wedding Rings cannot be sent via the Mail System. Messages which contain foul language cannot be sent. You cannot send mail to characters on the same account.
As of the 2/26/13 maint, the mail system will be disabled till further notice
As of the 4/10/13 maint, the mail system allows retrieval of mail until 4/16 after which ALL mail will cease to exist. Apparently, the in-game mail feature is being removed.