07.04.26, 20:57 +0100, der.hans: > Am 07. Apr, 2026 schwätzte Markus Schönhaber so:
>> 07.04.26, 18:29 +0100, Joe: >> >>> I'm fairly sure that neither the SMTP protocol nor exim in particular >>> distinguish cases in email addresses. I have a feeling I found this for >>> sure with exim4, but I've run it for so many years I can no longer >>> remember the details. >> >> I don't know anything about exim, but the SMTP protocol defines the >> local-part of an email address to be case-sensitive: >> >> | The local-part of a mailbox MUST BE treated as case sensitive. >> | Therefore, SMTP implementations MUST take care to preserve the case >> | of mailbox local-parts. In particular, for some hosts, the user >> | "smith" is different from the user "Smith". However, exploiting the >> | case sensitivity of mailbox local-parts impedes interoperability and >> | is discouraged. Mailbox domains follow normal DNS rules and are >> | hence not case sensitive. >> >> https://www.rfc-editor.org/rfc/rfc5321.html#section-2.4 > > Yes, officially local-part is case-sensitive, but in practicality it > should not be treated as case-sensitive. Yes, that's what the penultimate sentence in the paragraph I quoted from the RFC above says. > I haven't looked at exim for a long time, but it should default to > case-insensitive for delivery. I never had to change it, but that might > have been debian defaulting to useful configuration options. To comply > with the standard it should have to ability to be case-sensitive, but I'm > not going to complain if it doesn't. > > In the end, it's up to the local mail administrator, but case-sensitive > local-part is counter-productive. I don't doubt that. That's why the RFC discourages to insist on case-sensitivity of the local-part (see above). Nevertheless, you cannot presume that case of the local-part of an email address doesn't matter, even if all parts involved in the SMTP transaction comply to the standard. > Are you using any other tools in the delivery chain that might be doing > something case-sensitive? One example: Cyrus IMAP features a config setting lmtp_downcase_rcpt If you set that to 0, even if [email protected] reaches the mailbox, [email protected] might not. But I didn't want to spark a lengthy discussion about pros and cons of case sensitivity in mail addresses. I simply wanted to point out that Joe's claim that "the SMTP protocol [does not] distinguish cases in email addresses" isn't absolutely correct, and one shouldn't take it for granted that case doesn't matter, ever (even if it won't most of the time). -- Regards mks
