554 5.7.1 Service unavailable; client host rejected Email / SMTP Origin: Network Last updated 4 Nov 2026

SMTP: 554 5.7.1 Service unavailable; Client host [203.0.113.5] blocked / 554 5.7.1 <mail.example.com>: Client host rejected: Access denied

The server refused the connection from your IP because it is blocked by policy, not in the allowed list, or listed on a blacklist.

Exact message you may see 554 5.7.1 Service unavailable; Client host blocked554 5.7.1 Client host rejected: Access deniedClient host rejected: cannot find your reverse hostname554 5.7.1 Service unavailable554 5.7.1 blocked
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Seen on: SMTP

Meaning

Unlike a content rejection, 554 5.7.1 on connect refers to the connecting host. The remote admin has an IP allow/deny list, geo block, or uses a DNSBL. Check blocklists first, then contact the postmaster of the remote domain with your IP and the timestamp from the bounce.

Common causes

  • Your IP is on a DNSBL or the remote admin's deny list
  • Server accepts mail only from specific IPs
  • Missing or mismatched reverse DNS
  • Country/ASN-level block
  • Previous spam from the IP range

⚡ Quick fix

  1. Check your IP on blocklists (mxtoolbox.com/blacklists)
  2. Fix reverse DNS, SPF and DKIM
  3. Contact the recipient's postmaster with the bounce details

Detailed fix by platform

Linux

  1. host 203.0.113.5 (PTR must exist and match the HELO name) and dig +short TXT example.com for SPF

How to diagnose

  1. IP — Which IP is blocked?
  2. Lists — Listed anywhere?
  3. DNS — PTR and SPF correct?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Network. Errors that are often confused with or caused by this one (click to open):

421 4.7.0 Try again later (rate limited) — SMTP: 421 4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address. Mail sent from your IP address has been temporarily rate limited (Email / SMTP)421 4.7.0 Try again l…450 4.7.1 Greylisted, please try again later — SMTP: 450 4.7.1 <user@example.com>: Recipient address rejected: Greylisted, see http://postgrey.schweikert.ch/help/example.com.html (Email / SMTP)450 4.7.1 Greylisted,…451 4.3.0 Local error in processing — SMTP: 451 4.3.0 Error: queue file write error / 451 Requested action aborted: local error in processing (Email / SMTP)451 4.3.0 Local error…452 4.2.2 Mailbox full / over quota — SMTP: 452 4.2.2 The email account that you tried to reach is over quota (Email / SMTP)452 4.2.2 Mailbox ful…452 4.5.3 Too many recipients — SMTP: 452 4.5.3 Your message has too many recipients / 452 Too many recipients received this hour (Email / SMTP)452 4.5.3 Too many re…550 5.4.1 Recipient address rejected: Access denied — SMTP: 550 5.4.1 Recipient address rejected: Access denied. AS(201806281) [DB5EUR03FT015.eop-EUR03.prod.protection.outlook.com] (Email / SMTP)550 5.4.1 Recipient a…550 5.7.1 Blocked using zen.spamhaus.org — SMTP: 550 5.7.1 Service unavailable; Client host [203.0.113.5] blocked using zen.spamhaus.org (Email / SMTP)550 5.7.1 Blocked usi…550 5.7.25 PTR record required — SMTP: 550-5.7.25 The IP address sending this message does not have a PTR record setup, or the corresponding forward DNS entry does not point to the sending IP (Email / SMTP)550 5.7.25 PTR record…554 5.7.1…

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