Good morning I want to say a great "thank you" to all of you for the precious suggestions. All of your contributions will help us in the evaluation of a possible approach on this matter.
Regards Marco -----Original Message----- From: mailop <[email protected]> On Behalf Of Bill Cole Sent: mercoledì 27 febbraio 2019 18:27 To: Marco Franceschetti via mailop <[email protected]> Subject: Re: [mailop] deactivation of hard bounces On 27 Feb 2019, at 11:16, Marco Franceschetti via mailop wrote: > Hello, > > We at contactlab are considering a change in the deactivation of hard > bounces. > Currently, we suppress not existing mailboxes at the first hit. > > We are aware of a small percentage of false positives. > > Recent admissions criteria for Certified Senders states: > "The CSA sender must take email addresses from mailing lists, if, > after sending to this address, the mailbox is identified as > non-existent; at the latest, however, this must occur after three hard > bounces". > > We are evaluating to remove not existing mailboxes from the lists of > our clients after the second hit instead of the first one. > > Do you have any considerations, suggestions about this? There are subtle but important distinctions between types of "hard bounce" which you should take into account. ANY 5xy reply in SMTP (or asynchronous DSN message citing a 5xy reply) should be considered a "hard bounce." However, there are specific basic and enhanced SMTP reply codes which are direct explicit statements that an address is non-existent which should be honored immediately rather than taken as possibly mistaken and retested later with a different message. For example, a 550 reply to RCPT (or either stage of DATA, if there's only one accepted RCPT) without any enhanced status code should ALWAYS be treated as an indication of a non-existent address, as should 550 followed by any 5.1.x enhanced status code. It is debatable how other 5xy + 5.x.y combinations at various stages should affect sending a different message at a later time to the same address, but as every modern SMTP RFC has made clear: ANY 5xy reply should be considered a "hard bounce" for the specific transaction being tried. That means you must not try to resend the same message to the same address in any way: not 5 minutes later, not through a different outbound IP or to a secondary MX, not with a different envelope sender address, NOT AT ALL. It is good practice to remove an address from a list after just one hard bounce of the subset that clearly indicate that an address does not exist or after consecutive hard bounces (i.e. for different messages) with less certain meanings. Whether you make 2 or 3 your limit for hard bounce codes that might indicate problems other than address non-existence is unlikely to make much difference. -- Bill Cole [email protected] or [email protected] (AKA @grumpybozo and many *@billmail.scconsult.com addresses) Available For Hire: https://linkedin.com/in/billcole _______________________________________________ mailop mailing list [email protected] https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop _______________________________________________ mailop mailing list [email protected] https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop
