What are the key configuration settings for an MTA (e.g., Postfix, Exim)?

Every MTA requires core configuration to function properly and maintain deliverability. The essential settings:

Hostname and domain: Set myhostname and mydomain (Postfix) or equivalent. This identifies your server in SMTP conversations. The hostname should have valid forward and reverse DNS.

Network and relay settings: Define which networks can send through your server (mynetworks in Postfix). Restrict relaying to prevent becoming an open relay. Specify whether to relay through a smart host or deliver directly.

Authentication: Configure SASL for SMTP authentication if clients need to authenticate. This prevents unauthorized use of your server.

TLS encryption: Enable TLS for both inbound and outbound connections. Set certificate paths and minimum protocol versions. Modern configs should disable SSLv3 and TLS 1.0.

Queue settings: Configure queue directories, maximum queue lifetime, and retry intervals. Typical settings: 5-day queue lifetime, exponential backoff retries.

Rate limiting: Set connection limits and message rates to prevent abuse and avoid overwhelming recipient servers.

Logging: Enable detailed logging for troubleshooting. Log to syslog or dedicated mail log files.