Hi Pawel: Am 28.12.16 17:33 schrieb(en) Pawel Salek:
The goal seems sane. Have you got an idea how often the unwarranted rejection occurs?
First of all, a the issue can occur only if (1) the user requests a DSN *and* (2) the sending MTA includes the RFC 3461 ENVID parameter with the "MAIL FROM:" command *and* (3) the sending MTA fails to encode the '+' character according to RFC 3461, sect. 4 *and* (4) the receiving MTA verifies the parameter. As we construct the message-id from 43 base64-encoded characters, under the conditions above a /very/ rough estimate (i.e. uniform character distribution) for failure would be 43 / 64 = 67%. I used the obfuscated message-id since mid-February 2015 without any problem, and noticed the issue only about two weeks ago with one of my mail providers, probably after an update of either my or my provider's system. Interestingly, my Postfix (Ubuntu LTS) creates a broken ENVID, which is rejected by my provider's Postfix... The proposed base32 solution is a lot more robust, as only digits and upper-case ASCII letters are used. Cheers, Albrecht.
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