Why We Need to Han­dle Bounced Emails

Bounced emails are the bane of mar­ket­ing cam­paigns and mail­ing lists. In this ar­ti­cle, the au­thor ex­plains the na­ture of bounce mes­sages and de­scribes how to han­dle them.

OpenSource For You - - CONTENT -

Wikipedia de­fines a bounce email as a sys­tem-gen­er­ated failed de­liv­ery sta­tus no­ti­fi­ca­tion (DSN) or a non-de­liv­ery re­port (NDR), which in­forms the orig­i­nal sender about a de­liv­ery prob­lem. When that hap­pens, the orig­i­nal email is said to have bounced. Broadly, bounces are cat­e­gorised into two types: A hard/per­ma­nent bounce: This in­di­cates that there ex­ists a per­ma­nent rea­son for the email not to get de­liv­ered. Th­ese are valid bounces, and can be due to the non-ex­is­tence of the email ad­dress, an in­valid do­main name (DNS lookup fail­ure), or the email provider black­list­ing the sender/re­cip­i­ent email ad­dress. A soft/tem­po­rary bounce: This can oc­cur due to var­i­ous rea­sons at the sender or re­cip­i­ent level. It can evolve due to a net­work fail­ure, the re­cip­i­ent mail­box be­ing full (quota-ex­ceeded), the re­cip­i­ent hav­ing turned on a ‘va­ca­tion re­ply’, the lo­cal Mes­sage Trans­fer Agent (MTA) not re­spond­ing or be­ing badly con­fig­ured, and a whole lot of other rea­sons. Such bounces can­not be used to de­ter­mine the sta­tus of a fail­ing re­cip­i­ent, and there­fore need to be sorted out ef­fec­tively from our bounce pro­cess­ing. To un­der­stand this bet­ter, con­sider a sender [email protected] ex­am­ple. com, send­ing an email to [email protected] some­where. com. She mistyped the re­cip­i­ent’s ad­dress as [email protected] some­where. com. The email mes­sage will have a de­fault en­ve­lope sender, set by the lo­cal MTA run­ning there ( mta. ex­am­ple. com), or by the PHP script to [email protected] ex­am­ple. com. Now, mta. ex­am­ple. com looks up the DNS mx records for some­where. com, chooses a host from that list, gets its IP ad­dress and tries to con­nect to the MTA run­ning on some­where. com, port 25 via an SMTP con­nec­tion. Now, the MTA of some­where. com is in trou­ble as it can't find a user re­ceiver in its lo­cal user ta­ble. The mta. some­where. com re­sponds to ex­am­ple. com with an SMTP fail­ure code, stat­ing that the user lookup failed ( Code: 550). It’s time for mta. ex­am­ple. com to gen­er­ate a bounce email to the ad­dress of the re­turn- path email header ( the en­ve­lope sender), with a mes­sage that the email to [email protected] some­where. com failed. That's a bounce email. Prop­erly main­tained mail­ing lists will have ev­ery email pass­ing through them branded with the generic email ID, say [email protected] some­where. com as the en­ve­lope sender, and bounces to that will be wasted if left un­han­dled.

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