This morning we noticed some strange issues with email’s and delays in messages arriving. A quick check of the Exchange SMTP queues and the Mail Marshal queue found nothing, none of our messages were sitting on a server waiting to be delivered. I checked the queues 30min later and the Mail Marshal queue had blown out and had 80 messages from 70 domains waiting to be sent?!
A quick look at the mail history in Mail Marshal revealed the SMTP error, Data 421 Message rejected!
A quick search in Google found that the clever people on the Whirlpool forum had the problem solved. Dangermouze had found that the issue was with the Bigpond mail servers and their anti-spam settings. This started to make sense… a few weeks ago we added a secondary Internet connection to our Sonicwall firewall and configured the load balancing for the outgoing web requests. We had some issues with emails trying to go out on the new internet connection and failing because there was no reverse DNS and secondary MX server configured yet for that connection. Our workaround was to set the mail.bigpond.com server as our forwarding SMTP server which seemed to fix the problem, the Sonicwall would use our Telstra ADSL2 connection to send to this address and wouldn’t attempt to send mail on the Cable connection!
Word is that if too many emails are sent via the Bigpond mail server in a short period of time, they will temporarily block forwarding email from your address for 20min or so, then let you try again. This appears to be a restriction on the Bigpond Home ADSL plans, generally, BigPond Members can’t send more than 20 emails in 10 minutes and they can only be sent using the BigPond mail servers. however we’re on a Business Broadband connection, and appear to have the same limitation.
Dangermouze’s Telnet test to Bigpond SMTP
heres the a ‘telnet mail.bigpond.com 25’ session
220 oaamta03ps.mx.bigpond.com esmtp server ready wed,6 feb 2008 22:32
mail from: ***@bigpond.net.au
421 message rejected
The telnet session confirms that Bigpond is the source of the 421 message rejection, not the destination server or an RBL type service.
We may have to confirm out Bigpond settings with our account manager….