Spam filter / gateway
ZeroSpam SMTP Error Codes and Rejection Messages
ZeroSpam is a Canadian mail security gateway. Mail passes through its servers before delivery, recipients manage allowlists, and senders can reach its postmaster and abuse addresses for a closer look.
- Codes on record
- 2
- Responses
- 2
SMTP 4501 response
A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 450 across every provider
SMTP 5541 response
A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 554 across every provider
ZeroSpam bounce questions
›Why is ZeroSpam bouncing my email?
ZeroSpam is a Canadian mail security gateway. Mail passes through its servers before delivery, recipients manage allowlists, and senders can reach its postmaster and abuse addresses for a closer look. Match the exact wording of your bounce to one of the 2 responses on this page to find the specific reason and fix.
›How do I get past the ZeroSpam spam filter?
Authenticate with SPF, DKIM and DMARC, keep your sending IP and domain reputation clean, mail only engaged recipients, and honour unsubscribes. ZeroSpam also publishes postmaster guidance, linked on this page.
