> On 23 Jan 2025, at 17:55, Wietse Venema via Postfix-users 
> <[email protected]> wrote:
> 
> Gerben Wierda via Postfix-users:
>> I was wondering, suppose I have a user like this:
>> 
>> [email protected] is the account name
>> [email protected] is the incoming alias and the outgoing canonical
>> 
>> Could I force incoming mail to accept the alias form, but not
>> accept the account form? I.e. [email protected] as address is blocked,
>> but [email protected] is accepted and delivered to [email protected]
>> 
>> The spammers that send to my systems use the account form (and not
>> the alias/canonical) a lot, that's why I'm asking
>> 
>> I can of course create a new account form ([email protected]) and use
>> aliases/canonicals on that, but that might not take hold in the
>> long term and I would have to let users change their auth settings
>> (which now is user 'foo' and 'password')
> 
> Could this be as simple as an smtpd_recipient_restriction
> 
> /etc/postfix/main.cf
>    smtpd_recipient_restriction =
>       ...
>       reject_unauth_destination
>       check_recipient_access pcre:/etc/postfix/reject-account.pcre
>       ...
> 
> /etc/postfix/reject-account.pcre:
>    /^[^.]+@example\.com$/     reject must use the first.last form
> 
> Or the hard-core form:
> 
> /etc/postfix/main.cf
>    smtpd_recipient_restriction =
>        ...
>        reject_unauth_destination
>        check_recipient_access pcre:{{/^[^.]+@example\.com$$/ 
>               reject must use the first.last form}}
>        ...
> 
> If this is intended only for *some* accounts, then you need one
> to enumerate the forbidden forms.

If I understand the documentation correctly, this will reject (I'm planning for 
'discard' to get rid of the backscatter) the entire message for all recipients, 
including valid ones. If I want to discard it only for one of the recipients, I 
need to use the transport table. So, might it be enough to have a (non-pcre) 
entry:

[email protected] discard:

in the transport table? Discard is not mentioned in the man page for 
transport(5), but it is mentioned in th eman page for access(5)

Gerben

> 
>       Wietse
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