On 15/05/2025 16:30, John R Levine wrote:
On Thu, 15 May 2025, Alessandro Vesely wrote:
The SMTP extension is unsuitable in this case, ...
We gave up on the SMTP extension ages ago when someone pointed out that
large mail systems handle mail for many domains, some of which might do
DKIM2 and some of which don't, but you don't know the recipient domain
until RCPT TO which is much too late.
They might know the server name from ClientHello.
However, isn't this bad behavior? An SMTP extension signals the
capabilities of the receiving MX, regardless of the domain. Do they use
8BITMIME for some customers and not for others?
If DKIM2 specifies an SMTP extension, it should specify that signature
verification MUST be performed by servers that support that extension,
regardless of whether a domain adds DKIM2 signatures to its outgoing mail.
Or the extension may require the domain name as an EHLO parameter.
Best
Ale
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