Should transactional emails be sent from a different IP/domain?

Yes, separating transactional and marketing email infrastructure is a widely recommended best practice:

Why separate:

Marketing emails generate more complaints and can damage reputation. Transactional emails are critical (password resets, order confirmations) and must not be affected by marketing issues. Different engagement patterns require different reputation management.

Implementation options:

Separate subdomains: marketing.brand.com vs transactional.brand.com. Separate IPs: Dedicated IPs for each stream. Separate ESPs: Marketing platform for campaigns, transactional service for triggered messages.

Benefits:

Marketing problems do not impact transactional delivery. Easier to diagnose issues when streams are isolated. Reputation can be optimized for each stream's characteristics.

Transactional email is too important to risk. Isolation ensures that a marketing misstep does not prevent customers from resetting passwords or receiving receipts.