478:"As discussed in Section 7.8 and Section 7.9 below, dropping mail without notification of the sender is permitted in practice. However, it is extremely dangerous and violates a long tradition and community expectations that mail is either delivered or returned. If silent message-dropping is misused, it could easily undermine confidence in the reliability of the Internet's mail systems. So silent dropping of messages should be considered only in those cases where there is very high confidence that the messages are seriously fraudulent or otherwise inappropriate."
574:
76:
that it is allowed to receive has been reached. Additional situations in which a soft bounce appears is a block set up on the recipient's email to mark a certain sender as a 'spam' sender, or to blacklist a certain sender. Moreover, a temporary suspension of the recipient's email or a temporary error on the server are also causes of a soft bounce.
415:"If an SMTP server has accepted the task of relaying the mail and later finds that the destination is incorrect or that the mail cannot be delivered for some other reason, then it MUST construct an "undeliverable mail" notification message and send it to the originator of the undeliverable mail (as indicated by the reverse-path)."
158:, where a spammer (sender) may forge a message to another user (intended recipient of spam), and forges the message to appear from yet another user (a third party). If the message cannot be delivered to the intended recipient, then the bounce message would be "returned" to the third party instead of the spammer. This is called
42:
is a mature technology, counting more than thirty years, its architecture is increasingly strained by both normal and unsolicited load. The email systems have been enhanced with reputation systems tied to the actual sender of the email, with the idea of recipient's email servers rejecting the email
75:
Soft bounces are temporary. A bounced message that experiences a soft bounce may be tried to be redelivered at another time. Soft bounces happen when the recipient of the email has either a full Inbox and therefore no space to store another email is available, or a limit on the size of the emails
66:
Hard bounces are permanent and they score higher in terms of sender's IP damage. Hard bounces occur when the sender's mail server determines that there is a high likelihood that the recipient is unavailable and is likely to remain so. A few of the occasions when hard bounces occur are when the
67:
recipients of the email find themselves in one of the following situations: incorrect identifier/incorrect domain (such as a typo in the email address or in the domain) or their server does not accept emails anymore. In this case, removal of the email addresses that bounce back is mandatory.
121:
When sending an e-mail, the service from which the e-mail is sent may be unable to reach the destination address. In such case, the sender would receive a bounce message from their own mail server. Common causes for mail servers being unable to reach a destination:
92:
mail server reporting that although it had accepted the message, it is unable to deliver it to the specified user. When a server accepts a message for delivery, it is also accepting the responsibility to deliver a bounce message in the event that delivery fails.
23:
or just "bounce" is an automated message from an email system, informing the sender of a previous message that the message has not been delivered (or some other delivery problem occurred). The original message is said to have "bounced".
938:
232:
stated in the received mail which has triggered the auto reply, and this response is typically sent with an empty Return-Path; otherwise auto responders could be trapped in sending auto replies back and forth.
58:(ESPs) consider the total bounce rate as a decision factor when directing the email into a user's Inbox. Briefly, the total bounce rate is calculated as the sum of the hard bounce rate and soft bounce rate.
459:. Spam filters are not perfect. Rejecting spam based on content filtering implies giving to spammers a test environment where they can try several alternatives until they find content that passes the filter.
989:
Another method of defeating spam is to bounce mail back to them. This creates the appearance that your account doesn't exist and, if you're lucky, results in having your name removed from their lists.
420:
This rule is essential for SMTP: as the name says, it's a 'simple' protocol, it cannot reliably work if mail silently vanishes in black holes, so bounces are required to spot and fix problems.
375:(DSNs). DSNs can be explicitly solicited with an SMTP Service Extension, however it is not widely used. Explicit requests for delivery failure details is much more commonly implemented with
1027:
30:
More formal terms for bounce message include "Non-Delivery Report" or "Non-Delivery
Receipt" (NDR), "Delivery Status Notification" (DSN) message, or a "Non-Delivery Notification" (NDN).
382:
NDRs are a basic SMTP function. As soon as an MTA has accepted a mail for forwarding or delivery it cannot silently delete ("drop") it; it has to create and send a bounce message to the
483:
Not validating the sender is an inherent flaw in today's SMTP, which is without the deprecated source routes mentioned earlier. This is addressed by various proposals, most directly by
1007:
As you're probably aware, using Mail's Bounce command (Message > Bounce) isn't effective against spammers because nearly all the spam your receive carries a forged "from" address.
565:
RFC 3463 describes the codes used to indicate the bounce reason. Common codes are 5.1.1 (Unknown user), 5.2.2 (Mailbox full) and 5.7.1 (Rejected by security policy/mail filter).
178:
have accepted the message in the first place, and therefore would not have sent the bounce. Instead, it would have rejected the message with an SMTP error code. This would leave
511:
that allow users to "bounce" a message on demand. These user-initiated bounces are bogus bounces; by definition, a real bounce is automated, and is emitted by a MTA or MDA.
499:
There are many reasons why an email may bounce. One reason is if the recipient address is misspelled, or simply does not exist on the receiving system. This is a
537:
Typically, a bounce message will contain several pieces of information to help the original sender in understanding the reason their message was not delivered:
469:. Most times these are sent automatically from an infected machine. Since a bounce may contain a copy of the worm itself, it may contribute to its diffusion.
653:
may be used to report that value. Note that beside the numerical 3-digit value, the SMTP response contains itself a human readable part. The information
27:
This feedback may be immediate (some of the causes described here) or, if the sending system can retry, may arrive days later after these retries end.
201:. Auto-responses (automatic replies) are mails sent by a program—as opposed to a human user—in reply to a received mail and sent to the
150:
Users may receive erroneous bounce messages about messages they never actually sent. This can happen in particular in the context of
676:
while talking to smtp.store.example >>> RCPT TO:<nonexistinguser@store.example> <<< 550 No such user here
1032:
820:
278:
header fields inserted by other MTAs; this header field is generally guaranteed to reflect the last reverse path seen in the
995:
174:
mail server known that the message would be undeliverable (for instance, if Jill had no user account there) then it would
55:
217:
503:
condition. Other reasons include resource exhaustion — such as a full disk — or the rejection of the message due to
312:
to identify incorrect bounces based on the local part (left hand side before the "@") of the address in a non-empty
84:
Errors may occur at multiple places in mail delivery. A sender may sometimes receive a bounce message from their
634:
The second part of a DSN is also quite readable. It is essential to understand which MTA played which role. The
137:
with the destination address. For example, if the IP address is not assigned to a server, or if the server is
1052:
1022:
726:
720:
691:
484:
376:
353:
39:
440:
would hit an innocent third party. In addition, there are specific reasons why it is preferable to silently
309:
1057:
101:
When an e-mail arrives at the destination server for an address (such as mymail.example, when sending to
436:
s. It is then often impossible for the MTA to inform the originator, and sending a bounce to the forged
708:
410:, i.e. inform its originator. A bounce may arise also without a rejecting MTA, or as RFC 5321 puts it:
978:
896:
750:- Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs)
714:
702:
488:
294:
936:, "Managing delivery of electronic messages using bounce profiles", issued 2005-05-26
883:
225:
953:
456:
757:- The Multipart/Report Media Type for the Reporting of Mail System Administrative Messages
88:
mail server, reporting that it has been unable to send a message, or alternatively from a
8:
685:
320:, to identify auto replies. But the mail header is a part of the mail data (SMTP command
254:
245:
228:. These other auto replies are discussed in RFC 3834: auto replies should be sent to the
159:
852:
812:
138:
106:
816:
134:
910:
870:"Countering illegal traffic: A snapshot of monitoring and enforcement". 2016-09-27.
856:
934:
871:
844:
808:
594:
109:
is unable to deposit the message in the specified user's mailbox if the underlying
508:
110:
782:
775:
768:
761:
754:
747:
740:
598:
394:
Excluding MDAs, all MTAs forward mails to another MTA. This next MTA is free to
1047:
697:
462:
290:
202:
155:
1041:
466:
286:
198:
848:
835:
AferganMike; BeverlyRobert (2005-01-01). "The state of the email address".
263:
221:
127:
875:
130:
the destination address. For example, if the domain name does not exist.
573:
504:
429:
151:
593:
The format for the reporting of administrative messages is defined by
293:' was deprecated in 1989; for some historical background info see
54:. Both of them affect the IP reputation of the sender because the
785:- Internationalized Delivery Status and Disposition Notifications
626:
the original message, or a portion thereof, as an entity of type
379:(VERP), while explicit requests for them are rarely implemented.
771:- An Extensible Message Format for Delivery Status Notifications
911:"Hard Bounces vs Soft Bounces and how to remove them | Blog"
778:- Recommendations for Automatic Responses to Electronic Mail
602:
515:
297:. One special form of a path still exists: the empty path
301:, used for many auto replies and especially all bounces.
46:
Therefore, two types of email bounces have been created:
834:
116:
645:
rejects a message during an SMTP transaction, a field
428:Today, however, it can be common to receive mostly
285:Today these paths are normally reduced to ordinary
96:
954:"In the E-Mail Relay, Not Every Handoff Is Smooth"
638:is responsible for composing and sending the DSN.
561:Some or all of the content of the bounced message.
344:, or "reverse path") but not, e.g., the RFC 2822-
304:In a strict sense, bounces sent with a non-empty
186:) the obligation to create and deliver a bounce.
1039:
803:"Examples of rogue unsolicited email messages",
581:are named according to the point of view of the
544:The identity of the mail server that bounced it,
43:when a forged sender is used in the protocol.
1023:Mail DDoS Attacks through Non Delivery Messages
979:"Using Internet Applications in Mac OS X Tiger"
352:. These details are important for schemes like
623:lines that state several possible fields; and
494:
423:
240:is visible in delivered mail as header field
145:
976:
406:, etc. At this point the sending MTA has to
805:Security Risks in Social Media Technologies
316:, and it even defines a mail header field,
1028:Microsoft DSNs and NDRs in Exchange Server
541:The date and time the message was bounced,
518:are sent with the envelope sender address
837:ACM SIGCOMM Computer Communication Review
398:the mail with an SMTP error message like
389:
572:
558:The headers of the bounced message, and
1040:
977:Ray, William; Ray, John (2005-07-15).
951:
113:of the server has insufficient space.
16:Automated message from an email system
993:
547:The reason that it was bounced (e.g.
473:Quoting again RFC 5321, section 6.2:
117:Bounce due to unreachable destination
807:, Elsevier, pp. 241–242, 2013,
359:The remaining bounces with an empty
308:are incorrect. RFC 3834 offers some
252:) (which is usually combined with a
208:Examples of other auto replies are
13:
813:10.1016/b978-1-84334-714-9.50022-x
526:. They are frequently sent with a
432:emails, which usually uses forged
386:if forwarding or delivery failed.
79:
14:
1069:
1016:
994:Breen, Christopher (2006-01-27).
608:message composed of three parts:
324:), and MTAs typically don't look
218:challenge-response spam filtering
33:
764:- Enhanced Status Codes for SMTP
507:filters. In addition, there are
97:Bounce due to lack of disk space
743:- Simple Mail Transfer Protocol
733:
672:is sometimes reported as, e.g.,
165:
70:
61:
970:
952:Stross, Randall (2008-06-15).
945:
927:
903:
863:
828:
796:
585:. MTA names are often of type
189:
1:
789:
727:Variable envelope return path
721:Simple Mail Transfer Protocol
692:Bounce Address Tag Validation
612:a human readable explanation;
377:variable envelope return path
373:delivery status notifications
328:the mail. They deal with the
274:. The MDA also removes bogus
262:). The MDA simply copies the
7:
688:(Backscatter of email spam)
679:
457:Heuristically filtered spam
105:), it may be that the mail
10:
1074:
1033:Understanding Bounce Email
709:DomainKeys Identified Mail
495:Causes of a bounce message
424:Silently dropping messages
146:Bounce from forged message
568:
348:in the mail header field
655:
849:10.1145/1052812.1052822
715:Sender Rewriting Scheme
703:Sender Policy Framework
667:smtp;550Nosuchuserhere
617:message/delivery-status
534:at the recipient site.
295:Sender Rewriting Scheme
56:Email Service Providers
891:Cite journal requires
590:
481:
444:a message rather than
418:
390:Bouncing vs. rejecting
197:are a special form of
133:Unable to establish a
996:"Bouncing the creeps"
576:
475:
412:
244:inserted by the SMTP
1053:Email authentication
876:10.18356/0f24bf9f-en
365:non-delivery reports
332:, that includes the
103:alice@mymail.example
621:"name: type; value"
615:a machine parsable
577:MTAs involved in a
524:null sender address
514:Bounce messages in
289:, as the old SMTP '
255:mail transfer agent
246:mail delivery agent
1058:Internet Standards
958:The New York Times
662:smtp.store.example
601:. A DSN may be a
591:
530:header address of
408:bounce the message
299:MAIL FROM:<>
822:978-1-84334-714-9
270:command into the
1065:
1010:
1009:
1004:
1003:
991:
986:
985:
974:
968:
967:
965:
964:
949:
943:
942:
941:
937:
931:
925:
924:
922:
921:
915:bounceremove.com
907:
901:
900:
894:
889:
887:
879:
867:
861:
860:
832:
826:
825:
800:
666:
665:Diagnostic-Code:
663:
659:
606:multipart/report
533:
529:
521:
439:
435:
362:
351:
347:
343:
339:
336:address (a.k.a.
335:
323:
319:
315:
307:
300:
281:
277:
273:
269:
243:
239:
231:
226:feedback reports
182:mail server (at
1073:
1072:
1068:
1067:
1066:
1064:
1063:
1062:
1038:
1037:
1019:
1014:
1013:
1001:
999:
983:
981:
975:
971:
962:
960:
950:
946:
939:
933:
932:
928:
919:
917:
909:
908:
904:
892:
890:
881:
880:
869:
868:
864:
833:
829:
823:
802:
801:
797:
792:
736:
682:
677:
669:
668:
664:
661:
657:
647:Diagnostic-Code
571:
531:
527:
522:, known as the
519:
497:
437:
433:
426:
392:
360:
349:
345:
341:
337:
333:
321:
317:
313:
305:
298:
287:email addresses
279:
275:
271:
267:
241:
237:
229:
220:, replies from
192:
172:library.example
168:
148:
119:
99:
82:
80:Delivery errors
73:
64:
36:
17:
12:
11:
5:
1071:
1061:
1060:
1055:
1050:
1036:
1035:
1030:
1025:
1018:
1017:External links
1015:
1012:
1011:
969:
944:
926:
902:
893:|journal=
862:
827:
821:
794:
793:
791:
788:
787:
786:
779:
772:
765:
758:
751:
744:
735:
732:
731:
730:
724:
718:
712:
706:
700:
698:Email tracking
695:
689:
681:
678:
675:
674:
673:
656:
632:
631:
628:message/rfc822
624:
613:
570:
567:
563:
562:
559:
556:
545:
542:
496:
493:
471:
470:
460:
448:it (let alone
425:
422:
400:"user unknown"
391:
388:
318:Auto-Submitted
291:source routing
203:bounce address
191:
188:
167:
164:
147:
144:
143:
142:
131:
118:
115:
98:
95:
81:
78:
72:
69:
63:
60:
35:
34:Classification
32:
21:bounce message
15:
9:
6:
4:
3:
2:
1070:
1059:
1056:
1054:
1051:
1049:
1046:
1045:
1043:
1034:
1031:
1029:
1026:
1024:
1021:
1020:
1008:
997:
990:
980:
973:
959:
955:
948:
935:
930:
916:
912:
906:
898:
885:
877:
873:
866:
858:
854:
850:
846:
842:
838:
831:
824:
818:
814:
810:
806:
799:
795:
784:
780:
777:
773:
770:
766:
763:
759:
756:
752:
749:
745:
742:
738:
737:
728:
725:
722:
719:
716:
713:
710:
707:
704:
701:
699:
696:
693:
690:
687:
684:
683:
671:
670:
654:
652:
648:
644:
639:
637:
636:Reporting-MTA
629:
625:
622:
618:
614:
611:
610:
609:
607:
604:
600:
596:
588:
584:
583:Reporting MTA
580:
575:
566:
560:
557:
554:
550:
546:
543:
540:
539:
538:
535:
532:MAILER-DAEMON
525:
517:
512:
510:
506:
502:
492:
490:
486:
480:
479:
474:
468:
464:
461:
458:
455:
454:
453:
451:
447:
443:
431:
421:
417:
416:
411:
409:
405:
401:
397:
387:
385:
380:
378:
374:
370:
366:
357:
355:
342:Envelope-FROM
331:
327:
311:
302:
296:
292:
288:
283:
265:
261:
257:
256:
251:
247:
234:
227:
223:
219:
215:
211:
206:
204:
200:
199:autoresponder
196:
187:
185:
184:store.example
181:
177:
173:
163:
161:
157:
156:email viruses
153:
140:
136:
132:
129:
125:
124:
123:
114:
112:
108:
104:
94:
91:
87:
77:
68:
59:
57:
53:
49:
44:
41:
38:Although the
31:
28:
25:
22:
1006:
1000:. Retrieved
988:
982:. Retrieved
972:
961:. Retrieved
957:
947:
929:
918:. Retrieved
914:
905:
884:cite journal
865:
840:
836:
830:
804:
798:
734:Related RFCs
650:
646:
642:
640:
635:
633:
627:
620:
619:, a list of
616:
605:
592:
586:
582:
578:
564:
553:mailbox full
552:
549:user unknown
548:
536:
523:
513:
501:user unknown
500:
498:
482:
477:
476:
472:
449:
445:
441:
427:
419:
414:
413:
407:
404:"over quota"
403:
399:
395:
393:
383:
381:
372:
368:
364:
358:
329:
325:
303:
284:
266:in the SMTP
264:reverse path
259:
253:
249:
235:
222:list servers
213:
209:
207:
194:
193:
183:
179:
175:
171:
169:
166:Other causes
149:
120:
102:
100:
89:
85:
83:
74:
71:Soft bounces
65:
62:Hard bounces
52:soft bounces
51:
48:hard bounces
47:
45:
37:
29:
26:
20:
18:
686:Backscatter
658:Remote-MTA:
438:Return-Path
434:Return-Path
361:Return-Path
338:Return-Path
314:Return-Path
306:Return-Path
276:Return-Path
272:Return-Path
242:Return-Path
238:Return-Path
230:Return-Path
190:Terminology
160:backscatter
90:recipient's
1042:Categories
1002:2008-10-02
998:. Macworld
984:2008-10-02
963:2010-04-26
920:2020-05-14
790:References
643:Remote-MTA
384:originator
310:heuristics
214:challenges
152:email spam
135:connection
126:Unable to
111:hard drive
843:: 29–36.
781:RFC
774:RFC
767:RFC
760:RFC
753:RFC
746:RFC
739:RFC
334:MAIL FROM
282:command.
280:MAIL FROM
268:MAIL FROM
857:16604893
680:See also
649:of type
520:<>
330:envelope
210:vacation
170:Had the
641:When a
463:Viruses
212:mails,
195:Bounces
139:offline
128:resolve
992:, and
940:
855:
819:
729:(VERP)
723:(SMTP)
711:(DKIM)
694:(BATV)
597:
579:reject
569:Format
450:bounce
446:reject
396:reject
224:, and
180:Jack's
107:daemon
1048:Email
853:S2CID
717:(SRS)
705:(SPF)
528:From:
467:worms
452:it):
371:) or
258:, or
216:from
897:help
817:ISBN
783:5337
776:3834
769:3464
762:3463
755:6522
748:3461
741:5321
660:dns;
651:smtp
603:MIME
599:6522
516:SMTP
509:MUAs
505:spam
487:and
485:BATV
465:and
442:drop
430:spam
369:NDRs
363:are
354:BATV
350:From
346:From
326:into
322:DATA
236:The
50:and
40:SMTP
872:doi
845:doi
809:doi
595:RFC
587:dns
551:or
489:SPF
260:MTA
250:MDA
176:not
154:or
86:own
1044::
1005:.
987:.
956:.
913:.
888::
886:}}
882:{{
851:.
841:35
839:.
815:,
555:),
491:.
402:,
356:.
340:,
205:.
162:.
19:A
966:.
923:.
899:)
895:(
878:.
874::
859:.
847::
811::
630:.
589:.
367:(
248:(
141:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.