The mismatch between SNDS RCPT and DATA commands, without corresponding bounce messages, is a complex issue with numerous contributing factors. These encompass SMTP session management where multiple RCPT commands may exist for a single message, server-side techniques like greylisting and tarpitting which delay or reject connections, aggressive spam filtering silently dropping emails, network or server issues interrupting data transfer, deferred acceptance policies, and general SMTP errors. Microsoft also suggests RCPT counts reflect attempts and soft bounces, not just successful deliveries. These factors often prevent a standard bounce message, leaving a discrepancy in SNDS data.
10 marketer opinions
The discrepancy between SNDS RCPT and DATA commands without corresponding bounces arises from various factors beyond simple delivery failures. These include SMTP session management where a single message might have multiple RCPT commands for different recipients, greylisting causing retries, aggressive spam filtering silently dropping emails, deferred delivery due to temporary server issues, spam traps accepting recipients without processing the message, tarpitting delaying responses, connection timeouts interrupting data transfer, and silent discarding. These mechanisms lead to increased RCPT counts without corresponding DATA commands or bounce messages.
Marketer view
Email marketer from Mailjet explains that their servers often face situations with delayed responses during peak times. The RCPT command is accepted initially, but the server is unable to complete the data transfer in the appropriate timeframe. This leads to a mismatch.
4 Jul 2024 - Mailjet
Marketer view
Email marketer from Email Marketing Forum shares that some receiving mail servers employ greylisting, which temporarily rejects emails from unknown senders. This results in multiple RCPT attempts before a successful DATA transfer, leading to a mismatch in SNDS data.
5 May 2023 - Email Marketing Forum
3 expert opinions
The disparity between SNDS RCPT and DATA commands, in the absence of explicit bounce notifications, can be attributed to several factors. Microsoft explanations suggest RCPT represents attempted recipients while DATA indicates successfully delivered messages, or that RCPT includes soft bounces. Tarpitting, used to deter spammers, delays responses and can lead to senders abandoning the DATA transfer. Greylisting temporarily rejects emails, requiring retries that increment RCPT counts without always resulting in successful DATA delivery, especially if ultimate delivery fails silently.
Expert view
Expert from Email Geeks shares two possible explanations from Microsoft employees: One, RCPT is the number of attempted recipients, and DATA is the number of messages delivered. Two, RCPT could be higher as the result of a soft bounce (or attempted to deliver) and DATA was what they ended up accepting.
26 Sep 2024 - Email Geeks
Expert view
Expert from Word to the Wise explains that tarpitting, a technique used by recipient servers to slow down spammers, can cause RCPT commands to be higher than DATA commands. The server delays the response to the RCPT command, and if the sender gives up before sending the DATA, the counts will differ.
31 Oct 2021 - Word to the Wise
6 technical articles
Discrepancies between SNDS RCPT and DATA commands, without corresponding bounce messages, arise primarily due to network and server-side behaviors. Initial connection refusals lead to retries that increment RCPT counts, while only successful deliveries increment DATA. Network interruptions after RCPT but before DATA cause divergence. Deferred acceptance policies postpone data transfer, and if a failure occurs before DATA, a mismatch results. Standard SMTP protocols allow multiple RCPT commands before a DATA, and if RCPT commands fail subsequently or the connection breaks, discrepancies occur. Content filtering, size limits, authentication failures, and reputation problems can also cause DATA failures without triggering bounces.
Technical article
Documentation from Google describes various Gmail delivery errors, including cases where the RCPT command is accepted, but the DATA command fails due to content issues, authentication failures, or reputation problems. These failures might not always result in a standard bounce message.
13 Aug 2023 - Google
Technical article
Documentation from Microsoft explains that RCPT commands can be higher than DATA commands because the recipient server might initially refuse the connection. The sending server will retry delivery, incrementing the RCPT command count for each attempt, but the DATA command will only be incremented upon successful delivery.
16 Aug 2022 - Microsoft
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