Relay access denied

[rout3rx]

HI
Some our customers have a problem with emails,they have this error in undelivered mails:

Your message did not reach some or all of the intended recipients.

Subject: business description

Sent: 10/24/2013 16:16

The following recipient(s) cannot be reached:

'' on 10/24/2013 16:16

554 5.7.1 <>: Relay access denied


i think they use outlook
relay option in my plesk panel is : 20 min for pop3 and SMTP checked!
what can i do?
how can i fix this?

 

[Sven L.]

this can be caused by multiple things and you'll have to look closer into the maillog to find out what's going on.

things that i have seen causing this:
- if you have blackhole spam protection on, using for example xen.spamhaus.org (too agressive) and the client has dynamic IP
FIX: either don't use blackhole at all or use a less agressive one
- if you use greylisting and they have their own exchange server or use outlook.com
FIX: add *.messaging.outlook.com to server wide whitelist
- if the client is not properly authenticating. pop3 authentication doesn't really work well with outlook and i have it make touble on iphones too.
FIX: the best is to use SMTP authentication and make sure clients enable smtp auth in their outlook and fill in the proper fields in their iphone config.