Re: [exim] Sender verification failing sometimes

On 2011-06-13 at 00:32 +0000, Michael Jimenez wrote:
> So I've been looking at my mail server mainlog for the past couple of days watching mail come in and out, I've noticed that this Microsoft address keeps failing to verify:

You're using sender *callout* verification to systems not under your
administrative control. This is regarded by many as abusive, and will
get you placed on various blacklists.

The larger providers have rate-limits and other DoS filters; so when an
MSN address is spoofed and you keep hitting their mail-servers with
checks on mails they didn't send, you'll exceed ratelimits and get
fast-failed: they're rejecting you attempting to deliver to them, which
you're interpreting to mean that the address is invalid.

Sender callouts are best suited for use to systems under your own
control.