How Email Relay Keeps You Online During Provider Outages
Your mail server goes down. Maybe it is planned maintenance, maybe it is an unexpected outage, maybe your hosting provider is having a bad day. During that downtime, what happens to your incoming email?
Without a relay: emails bounce
When a sending server tries to deliver email to your domain and your mail server is unreachable, one of two things happens:
- Immediate bounce (5xx): The sending server gets a permanent error and returns the email to the sender as undeliverable. The email is lost.
- Temporary failure (4xx) + retry: The sending server queues the email and retries. Most sending servers retry for 1-3 days. If your server is still down after that, the email bounces permanently.
The problem: you have no control over the sending server's retry policy. Some servers retry aggressively for days. Others give up after a few hours. And you never know which emails were lost.
With a relay: emails queue safely
When you use Cleanbox Relay, your MX records point to Cleanbox, not directly to your mail server. The flow becomes:
- Email arrives at Cleanbox (always available)
- Cleanbox filters spam, scans for viruses, applies your rules
- Cleanbox tries to forward clean email to your mail server
- If your server is down, Cleanbox queues the message and retries with exponential backoff
- When your server comes back online, queued messages are delivered automatically
The critical difference: Cleanbox's retry queue holds messages for up to ~4 days with 11 retry attempts. During that entire window, the sending server already got a success response from Cleanbox — it thinks the email was delivered. No bounces. No lost messages.
Real-world scenarios
| Scenario | Without relay | With Cleanbox Relay |
|---|---|---|
| Server maintenance (1-2 hours) | Some emails bounce, some queue at sender | All emails queued, delivered after maintenance |
| Hosting outage (4-8 hours) | Most emails bounce permanently | All emails queued and delivered when resolved |
| Extended outage (1-2 days) | All emails bounce | All emails queued (within 4-day window) |
| Migration to new server | Risk of lost email during DNS propagation | Update relay destination; zero email loss |
Server migration without email loss
One of the most valuable use cases for relay is server migration. When you move to a new mail server:
- Set up the new server
- In Cleanbox Relay, update the SMTP destination to the new server's hostname and port
- Test delivery to the new server
- Done — no MX record changes needed, no DNS propagation delay, zero email loss
Without a relay, migrating requires changing MX records (24-48 hour propagation) during which some email goes to the old server and some to the new one. With a relay, the MX records stay pointed at Cleanbox and you just change where Cleanbox forwards to.
Monitoring delivery status
In the Cleanbox dashboard, you can monitor delivery status in real time:
- Delivered: Successfully forwarded to your server
- Pending: In the retry queue, waiting for next attempt
- Failed: Exhausted all retry attempts after ~4 days
If you see messages accumulating in "pending" status, your mail server may be down. Fix the issue and pending messages will deliver automatically on the next retry cycle.
Relay is available on the Advanced ($35/mo) and Enterprise ($100/mo) plans. See Setting up Relay to get started.
