SMTP: 4.x.x — Transient Failures
Deferrals: greylisting, rate limits, full mailboxes. The sender should retry.
8 live · ~180 planned · Source: RFC 5321 reply codes + RFC 3463 enhanced status codes (IANA registry)Click a card for a quick view. The full page has every fix.
130×100
Ad · Carbon / EthicalAdsDeveloper ad slot. 330×132 reserved, zero layout shift.