550 g_spam_allow_disable: SPF failure or RBL listing detectedWhat does 550 g_spam_allow_disable mean?
g_spam_allow_disable is an internal flag used by Tucows’ MTA infrastructure (Hover, OpenSRS, EnomMail, and other Tucows email products). When this flag fires, the MTA has determined that the sender fails one of two conditions: SPF validation, or appears on a public RBL the Tucows engine queries (typically Spamhaus, Barracuda, Abusix). The rejection is a hybrid signal: fix either SPF or the RBL listing and retries succeed. Tucows does not publicly document which RBLs they query or expose lookup endpoints, so diagnosis requires checking major DNSBLs in parallel with auditing SPF.
Is this a soft or hard bounce?
Two potential causes, one wrapping. Check SPF first (faster fix), then audit public DNSBLs. Either resolution unblocks delivery to Tucows-hosted domains.
Common causes
Most common cause. Sending domain has no SPF, or sending IP not in SPF policy.
IP on Spamhaus, Barracuda, or Abusix. Tucows queries these as part of g_spam_allow checks.
Permerror from malformed SPF or excess DNS lookups treated as fail.
How to fix it
Run dig TXT yourdomain.com. Confirm SPF record exists, includes your sending IP, and uses -all or strict ~all. Test at kitterman.com.
Look up your IP at Spamhaus, Barracuda, Abusix. Address any listing through the standard removal procedures.
Once SPF passes OR DNSBL clears, queue retries to Tucows-hosted domains will succeed.
Provider-specific notes
| Tucows brand | Notes |
|---|---|
| Hover | Tucows consumer registrar with hosted mail. |
| OpenSRS | Wholesale registrar with mail products used by many resellers. |
| EnomMail | Enterprise mail product through Enom (Tucows-owned). |
| Resellers using Tucows infrastructure | Many small registrars white-label Tucows mail. All share g_spam_allow logic. |
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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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