Fixing "4.4.7 message expired" / retry timeout exceeded

4.4.7 means your server kept trying to deliver and eventually hit its retry limit. The 4 class is temporary, but after enough failed attempts the message is returned as expired. This almost always points at the destination, not you.

What it means

For the whole retry window (often a day or two) the recipient server was unreachable or deferred every attempt. The final notice is your MTA giving up, not a permanent policy rejection.

Why it happens

The recipient mail server was down, a firewall blocked the connection to its MX, or aggressive greylisting/throttling deferred every attempt. Occasionally the recipient MX record itself is broken.

Diagnose it

Use the SMTP diagnostics tool to see whether the recipient MX answers on port 25 right now, reads a banner, and offers STARTTLS. If it does not connect, the destination is the problem.

Fix it

1. Confirm the recipient MX is reachable now — if it is, simply re-send; the earlier outage has passed.

2. If it is your own inbound server, make sure it is running and accepting connections on port 25.

3. Verify the recipient domain’s MX points to a host that resolves and answers (see the no-MX guide).