Eugene Podshivalov:
> When reject_unverified_sender param is set and an email is sent on behalf
> of the server the double-bounce check is still performed (i.e. sent to
> itself).
What is 'the double-bounce check'?
Postfix probes use a sender address that does not receive email.
There is even a feature to make the probe sender time-dependent,
to limit the impact of spam.
Wietse
address_verify_sender_ttl (default: 0s)
The time between changes in the time-dependent portion of address veri-
fication probe sender addresses. The time-dependent portion is appended
to the localpart of the address specified with the address_ver-
ify_sender parameter. This feature is ignored when the probe sender
addresses is the null sender, i.e. the address_verify_sender value is
empty or <>.
Historically, the probe sender address was fixed. This has caused such
addresses to end up on spammer mailing lists, and has resulted in
wasted network and processing resources.
To enable time-dependent probe sender addresses, specify a non-zero
time value (an integral value plus an optional one-letter suffix that
specifies the time unit). Specify a value of at least several hours,
to avoid problems with senders that use greylisting. Avoid nice TTL
values, to make the result less predictable. Time units are: s (sec-
onds), m (minutes), h (hours), d (days), w (weeks).
This feature is available in Postfix 2.9 and later.
