| AL | Always. All MFA segments (whether denoting errors or not) must be returned via the application-level acknowledgment message |
| ER | Error/Reject conditions only. Only MFA segments denoting errors must be returned via the application-level acknowledgment for this message |
| NE | Never. No application-level response needed |
| SU | Success. Only MFA segments denoting success must be returned via the application-level acknowledgment for this message |