Margin is the funds in your account used as collateral for your derivative positions.
Initial margin is the minimum amount of margin required to open a position. Initial margin is often abbreviated to IM.
Any order or open position requires initial margin. If the account does not have enough margin balance to cover the initial margin requirements, there can be no new orders placed that would increase the margin usage. Orders that reduce the margin usage can still be placed.
If the initial margin usage exceeds 100%, the available balance would show as 0.
In certain portfolios closing an existing position on a particular instrument could increase the margin usage of the account, because that instrument is hedging a position in another instrument.
If the initial margin usage exceeds 100%, an automated email is sent to the account holder. However, there is a limit to how many of these emails will be sent per day. These emails are designed to be a helpful reminder, but should not be relied upon for risk management.
Maintenance margin is the minimum amount of margin required to keep a position open. Maintenance margin is often abbreviated to MM.
Any open position requires maintenance margin. If the account does not have enough margin balance to cover the maintenance margin requirements, the positions will be incrementally liquidated. The details of the liquidation process depends on the margin model used on the account. While the maintenance margin usage exceeds 100%, and therefore liquidation is in progress, the account holder will not be able to adjust the portfolio themselves.
If the maintenance margin usage exceeds 100%, an automated email is sent to the account holder. If the maintenance margin usage exceeds 100% several times in a short space of time, an email may only be sent for the first occurrence. These emails are designed to be a helpful reminder, but should not be relied upon for risk management.