Hi!
We’re planning to run a small inbound-only SMTP server on Fly to receive image attachments from old game cameras for our service. Some old cameras only support TLS 1.0/1.1 or plain SMTP on port 25, so we cannot route them through Resend Inbound which we currently use for modern cameras.
Planned setup:
- Separate Fly app (Node.js / Haraka SMTP server), dedicated IPv4
- Listening on TCP 25, 465, 587 — all inbound only
- AUTH PLAIN/LOGIN required on every port (no anonymous relay)
- We do not send any outbound mail from this app — transactional email continues via Resend
- Per-tenant credentials, rate-limited per credential and per source IP
- Estimated volume: a few hundred messages per day total across all pilot users
Questions:
- Is inbound port 25 allowed on Fly with a dedicated IPv4? If not officially supported, are there policy constraints we should be aware of?
- Are there abuse-detection thresholds we might trip with SMTP-shaped traffic (vs. HTTP)?
- Do you assign clean IPs from non-blacklisted ranges, or should we request one? (Less critical since we’re inbound-only, but relevant for sender SPF checks.)
- Is the standard [[services]] config in fly.toml sufficient for these ports, or do we need a different setup?
If port 25 inbound is not feasible on Fly, we’ll move this app to a VPS elsewhere — please just let us know directly.
Thanks!