Bounce analyzer
Paste a bounce and get what each code means and how to fix it.
The lookup needs JavaScript. Every code in the wiki is also listed as a plain link.
The whole bounce works best: the lookup picks out the reply code, the enhanced code and any provider tag, and reads the wording for who sent it. A code on its own works too, such as 550 5.1.1, 421 or TSS04.
What is a bounce message?
A bounce message, or non-delivery report, is the email your own server sends back when another server refuses a message. It quotes the receiving server's reply: a three-digit SMTP reply code, usually an enhanced status code such as 5.7.26, and a line of text. Its structured form, the delivery status notification, is defined in RFC 3464.
Reading the result
Paste the whole bounce or just the code. The analyzer lists the codes it found and the provider the wording points to, then the entries in the error code wiki that explain them, best match first, each marked temporary or permanent. Open one for the causes, the fix in order and its sources. Nothing you paste leaves your browser.
Every entry it opens is a page in the error code wiki, written from the standard or the provider's own documentation and linked to it. Beat watches for the causes behind the common ones, across all 41 checks and 33 blacklists.
Common bounces it explains
Mail that failed authentication
Gmail answers 550 5.7.26 when a message passes neither SPF nor DKIM, or fails the DMARC policy of its From domain. The fix is in your DNS records, not in the message.
An address that does not exist
550 5.1.1 means the receiving domain has no such mailbox. Remove the address from your list: sending again to addresses that bounce this way counts against you with the receiver.
Deferrals and rate limits
A 421 is a request to slow down, such as Gmail's 4.7.0, Microsoft's 4.7.500 or Yahoo's [TSS04] over volume or complaints. Your server keeps the message and retries, and pushing more mail at it usually makes the deferrals last longer.
A block on your sending IP
Microsoft's S3140 and S3150 mean the sending IP is on one of its own block lists, and other providers often name a public blocklist in the text. Check the IP with the blacklist checker, then ask for removal where it is listed.
Read next
More tools
Resolve and validate an SPF record, including the 10-lookup limit.
DKIM LookupFind and inspect DKIM public keys on any selector.
DMARC LookupRead a DMARC policy and judge how much it actually protects.
MX LookupList mail exchangers with priorities and resolved addresses.
BIMI LookupCheck a BIMI record and whether its logo and VMC qualify.
PTR LookupReverse-resolve a sending IP and check forward-confirmed rDNS.
A heartbeat for your email.
Beat runs every check on this site on a schedule: 41 checks, 33 blacklists and real inbox placement. The moment something breaks, it tells you what broke, why it matters, and the exact fix.
- SPFpass
- DKIMpass
- DMARCp=none
- Blacklists0 of 33
Illustrative. Your domain, every few hours.
Also from us:Pulse: your own sending infrastructureConsulting: $65/hr, no retainer