Jeroen van Aart wrote:
> Thought you'd like to know.
>
> To quote
> http://projects.puremagic.com/greylisting/whitepaper.html?view=markup:
>
> "One issue is that some MTA software (Exim for example) attempts to
> limit the problem of forged sender addresses by attempting to verify
> that the claimed sender of an email is a valid address by doing an SMTP
> callback before accepting mail. Since it is desired to minimize the
> traffic when a mail may be rejected temporarily, the best course of
> action would be to issue a tempfail after the RCPT command. However, in
> the case of a SMTP callback, doing so at that point may cause our
> outgoing mail to be delayed unnecessarily."
>
> I don't think exim does that by default (anymore?). It could get you
> blacklisted someone wrote here recently.
>
Indeed, exim doesn't so that _by default_. However callouts may be
useful in some cases, and only makes your mail delayed, not denied.
The point is callouts are useful, but you must restrict them to
suspicious mails, not use them as your first ACL.
Generally, very badly configured servers, for example those who greylist
every mail even if you already sent them one, are the only ones to cause
real delays.
