550 Blocked by ivmSIP and/or ivmSIP/24 (see https://www.spamrats.com)What does 550 Blocked by ivmSIP and/or ivmSIP/24 mean?
ivmSIP and ivmSIP/24 are DNSBLs operated by Spamrats that list IPs (ivmSIP) and entire /24 subnets (ivmSIP/24) identified as sending spam without proper RFC compliance: HELO format violations, missing or generic PTR records, sending from dynamic ranges, or pattern-matching to known spam infrastructure. The /24 variant penalizes the entire subnet when a critical mass of listings accumulates on neighboring IPs, which can affect senders who share infrastructure with abusive neighbors. Removal is self-service at Spamrats once the underlying configuration issue is resolved.
Is this a soft or hard bounce?
Most ivmSIP listings come from PTR record problems (missing, generic, or non-FCrDNS) or HELO format violations. Fix the configuration first, then delist.
Common causes
No reverse DNS or a generic hostname like x.x.x.x.dynamic.isp.example. ivmSIP penalizes IPs without proper sending hostnames. See 550 client rejected: no rDNS.
Spamrats lists IPs in known dynamic or residential blocks. The fix is to use an authenticated SMTP relay.
Sending HELO with bare IP, generic hostname, or non-FQDN format. Configure HELO to a valid FQDN matching the PTR record.
The ivmSIP/24 zone lists entire subnets when many IPs in the same /24 are flagged. Contact your hosting provider if neighboring IPs are abusive.
How to fix it
Go to spamrats.com/lookup.php and submit your IP. The result shows which Spamrats zones list your IP.
Set a proper PTR record matching a real sending hostname. Configure HELO to the same FQDN. If sending from a dynamic IP, switch to an authenticated SMTP relay.
Spamrats self-service delisting is on the lookup page. Removal is automated and typically processes within minutes when the PTR/HELO configuration is correct.
Include ivmSIP and ivmSIP/24 in your blocklist monitoring alongside Spamhaus, Barracuda, and Abusix.
Provider-specific notes
| MTA | Behavior |
|---|---|
| Postfix with Spamrats | Configured via reject_rbl_client dyna.spamrats.com or noptr.spamrats.com. Returns 550 with the Spamrats URL in the rejection text. |
| Exim with Spamrats | Returns 550 when ivmSIP or ivmSIP/24 appears in an ACL deny condition. |
| Generic | Spamrats is widely used by small-to-medium MTAs and some hosting providers due to its self-service removal model. The /24 variant catches more cases than the per-IP version. |
Related error codes
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About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
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