I've been having a few peculiar problems since switching from Merak to SmarterMail. The first problem is that some clients have their emails bounce back with the following message: 550 5.7.1 Client host rejected: cannot find your hostname I'm pretty sure this has to do with reverse lookup, but if you take a look at this dns report: http://www.intodns.com/maebrunkendesign.com, you will see that my Reverse MX A records are resolving. Granted, they seem to resolve to 3a.ee.85ae.static.theplanet.com (which is the company that hosts my server), but does it have to resolve to the same domain as the sending email (*@maebrunkendesign.com)? The other problem, which may be related, is that yahoo mail seems to be delaying deliveries from all the domains on my server: [*][*][*]<style> Reason: Remote host said: 421 Message from (18.104.22.168) temporarily deferred - 4.16.50. Please refer to http://help.yahoo.com/help/us/mail/defer/defer-06.html This looks like they are graylisting, but even when messages are successfully delivered hours (sometimes days) later, The same process has to be repeatedwhen sending subsequent emails. The end result is that every email sent to yahoo since I started using smartermail is delayed. What could be the problem? Please help!