What the receiver is telling you

Your server tried to connect to the recipient's MX and got no answer — the host is down, port 25 is firewalled, or the MX record points at something that is not a mail server. Servers retry automatically for a day or more. A single 4.4.1 is noise; a domain that returns nothing but 4.4.1 for two days has a broken MX, and the mail will eventually expire as a 5.4.7.

How to handle a soft bounce

Your server or sending tool retries soft failures automatically, usually for one to three days. Most clear on their own. The mistake is leaving an address that soft-bounces on every step in an active sequence: each attempt is logged, and a mailbox that has been full or unreachable for two weeks is not going to read a follow-up. Three consecutive soft failures is the point to remove it. Track soft bounces separately from hard ones; they are a different signal and receivers weight them differently.

What to do

1. Do nothing for the first day; retries handle transient outages.
2. If it persists, look up the domain's MX and try connecting to it on port 25 — a hostname that does not resolve, or resolves to a web server, is the cause.
3. If every domain is timing out, the problem is yours: outbound port 25 blocked, or your relay is down.

don't Do not remove the address on the first timeout. It says nothing about the mailbox.

Decode the whole bounce

Paste the complete failure notice — every code and the receiver's wording — and get each part explained together.

Common questions