How do I manage IP addresses and rotation with an MTA?

Managing multiple IP addresses allows you to segment traffic, distribute load, and isolate reputation. MTAs provide several methods:

Binding to specific IPs: In Postfix, use smtp_bind_address to set the default outbound IP. For per-destination control, create transport maps that specify different IPs for different recipient domains or message types.

Transport maps: Define custom transports in master.cf, each bound to a different IP. Then use transport_maps to route messages through specific transports based on rules.

Example transport in master.cf:

marketing unix - - n - - smtp -o smtp_bind_address=192.0.2.10

transactional unix - - n - - smtp -o smtp_bind_address=192.0.2.11

IP rotation: For load distribution across multiple IPs, use a round-robin approach. Some MTAs support this natively; others require external load balancers or scripts that modify transport assignments.

PowerMTA offers sophisticated IP management with automatic rotation, warmup schedules, and per-domain IP selection rules built in.

Keep IPs separated by mail type. Marketing and transactional streams should use different IPs so reputation issues in one don't affect the other.