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Store and forward

Discussion in 'E-mail Discussions' started by santrix, Feb 10, 2009.

  1. santrix

    santrix Well-Known Member

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    Hi,

    I am running release build WHM/Cpanel on Centos VPS.

    I have a client who is running their own MS Small Business Server for e-mail. I have put their server IP as the lowest cost MX - but would like the VPS to act as a backup in case their server goes down.

    I'm not entirely clear on how mail servers interact. If messages get delivered to our VPS, then will they then be relayed to the lowest cost MX server when it comes back up? If not, is there a way within Cpanel, or just by editing config files to set up this kind of routing? Any help appreciated.

    The other option is just to set up a POP connector on the customer's SBS machine to mop up anything that arrives on our server every 15 minutes.

    Thanks for any advice.
     
  2. brianoz

    brianoz Well-Known Member

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    It's best to just set them up as primary MX and not include a secondary.

    The SMTP protocol has built into itself mandatory retry requirements, so even if the mail server is down email will be queued and retried. After 4 hours, people sending them email will get a warning that there was a delay, and after 4 days the retries will stop and they get a message saying the email failed.

    If you use a secondary, it becomes a primary target for spammers and it becomes hard to drop the spam unless you know which users are valid (sure, you can use spamassassin at SMTP, or something similar, and you can use RBLs, but at the end of the day, some gets through). Spammers actually look for secondary MXes and deliberately target them. Also, the risk of losing email RISES with a secondary as you are more likely to experience a configuration failure over the long haul - secondaries don't get checked often.

    As another topic, if you want to protect their Exchange from outside visibility, you can create a forwarding mechanism on the server using instructions from the FAQ at www.configserver.com. Or if you want to go heavy duty, you can use Google message filter.

    There's also a handy technique called "nolisting" that relies on spammer behaviour to efficiently drop about 40-60% of spam. Goes well with an MX to an exchange server.
     
  3. rhenderson

    rhenderson Well-Known Member

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    BrianOz is right about the spammers going up the list to send spam. We demoed an account at rollernet.us and it works well and has spam controls for a backup MX, it is also the cheapest we have found.
     
  4. santrix

    santrix Well-Known Member

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    Brianoz, yes, I thought about nolisting... I used to do it when i used junkemailfilter for a while. I can't find the configserver page that specifically talks about their own mail forwarding ideas?

    The backup POP3 mailbox does run through spamassassin, but yes, I can see that it may get a hammering.It shouldn't be left to get full though, as the customer's SBS server should collect mail from it every 15 minutes.

    Rollernet looks interesting. Rhenson, I'd be interested to know how long you have been using it, what kind of throughput it is seeing, the false positive rate from the spam filtering, and performance in general... it may be what we're looking for.

    Steve
     
  5. rhenderson

    rhenderson Well-Known Member

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    Steve,

    We used the Rollernet free account until we used up the 100MB, took around 3 weeks. Our mailserver did not go down, so the 100MB was all spam. Knowing that I cannot speak to false positives but it blocked the majority of that spam. The real thing I discovered was how many spammers use the higher MX record for spamming.

    Three or four years ago we setup a "mailserver" using nix and postfix as the mailserver. It was going to be a primary MX and spam scanner, which left the regluar server as the backup MX, seemed like a perfect setup. Postifx was easy to relay mail based on a domain list we have rsync setup to keep the list current with our server. All the mail went to this server and was scanned. It took out most of the spam but some got through (was using exim and SA) then it relayed to our server where we setup up Exim and MailScanner) Mailscanner caught a lot of the remaining spam. It did help with the load but in the end it proved to be a bigger pain than it was worth.

    From what I understand cPanel 11.25 or some other later number is suppose to have mail and mysql clustering. Because of and the improvments cPanel made with cPanel 11 we went back to a standard way of doing things and are just waiting for the cPanel version that allows clustering of those services.
     
  6. xyzed

    xyzed Member

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    If you do go for a secondary MX, 1 trick is to create the final one as a dummy so spammers targetting the highest MX will go nowhere.

    But as long as the DNS is up, then thats a less headache way with the sender just receiving a rety.
     
  7. brianoz

    brianoz Well-Known Member

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    As mentioned a few posts back above, this is called "nolisting".

    A better technique than just listing a dummy non-responsive MX for the highest is to have three (3) MX listings - the lowest and the highest being a dummy. I have the lowest on immediate deny (TCP reset) and the highest on slow deny (DROP - takes 1 minute or so, as only spammers use the highest). This works very well.
     
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