Is this a normal or common Email performance?

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Posted by jagarco, 05-25-2015, 04:12 PM
Hi I've had a Reseller account with this Host for like 10 years, everything's great. But in the last months, some customers have reported not receiving emails from their contacts, we've checked bounced back errors and their contacts's servers are Blacklisted. It is like this 90% of the times(10% being overquota or account nonexistent related) We've only whitelist those domains on our server to let them in but also tell our customers that their contacts need to check with their Host or email provider to fix their issue. Unfortunately, our customers don't like that they have to ask their contacts for errors replies just to tell them(our customers) we're not receiving emails from anyone else in the same situation, except the domains we've whitelisted, which is almost useless. BUT, in the last 10 days, things got worse, some Blacklists shut down and our server was just getting false positives, our customers complaining there's something wrong as their incoming email simply stopped flowing, we notify our Host and they update the Email setup. Problem is, our customers still "feel" like 80% decrease in the amount of incoming email. Customers are fed up and don't want to deal with more asking for errors replies to their contacts or whatever, they just say "we're still having problems". Last info from our host was that they double checked Email service and that there's no faulty nor false positive in the Antispam layer, everything is normal. So, maybe, our customers (like 2 or 3 of them) are paranoid and they're getting all the legitimate emails except the bunch of Spam they were used to 10 days a go. There has also been a virus around that may have got lot of Servers Blacklisted, hence the decrease in the incoming email. So, is it normal or common practice to use 3rd part Blacklists as Antispam strategy? If so, is my Host using a not so optimum list of Blacklists Setup?
Posted by steven99, 05-25-2015, 05:35 PM
There was a post similar to this on reddit's /r/sysadmin subreddit where the resolver the mail server was using was returning the wrong result for a DNS RBL lookup. Basically, the resolver was returning a result when it should have returned NXDOMAIN. So for example, if you do 1.1.1.1.bl.spamcop.net, you should get a NXdomain but if you get 127.0.0.2 or another result your anti-spam system may then flag it as being on a RBL. As such, make sure that your resolvers are returning proper results and not a result that will throw the anti-spam system off.