Am 07. Apr, 2026 schwätzte Markus Schönhaber so:
moin moin,
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.
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.
Are you using any other tools in the delivery chain that might be doing
something case-sensitive?
ciao,
der.hans
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