Multiple email domains on 1 global IP

[TiziteLayinLow]

I have several websites that I host - very small sites. I have email accounts setup for them. These all come from 1 server on 1 RR connection.

I was told that spam filtering is partly done in reverse looksup..

example:

1st domain - @matt.com
2nd domain - @andy.com

when user@matt.com sends email to user@aol.com .. aol email server says.. ok what is IP for matt.com? .. answers 10.233.23.2.. now what is domain name for 10.233.23.2.. answers.. 10.233.23.2@rr.com.. when these servers see that the domains don't match they assume that it is spam.

Now the problem lies when you have multiple domains on 1 global IP.

@matt.com email goes out.. goes to IP.. goes back to domain.. gets matt.com (say I set this with RR)..

then @andy.com email goes out.. goes to IP.. goes back to domain.. gets matt.com and says SPAM.. lol

there has to be a way to get this resolved.. what do the email hosting companies do? I know with RR business class I can get multiple global IP addresses and set a PTR for each but I would rather not do that.. example..

@myonlinestore.com
@myonlinestore.net
@myonlinestore.info
etc

all on the same email server if they can send out with these domains as well as recieve then only 1 wont get classified as spam...

any help with this issue is greatly appreciated. I do not want to beat the spam filters I just want to know how to host numberous email domains without getting tossed email.

thanks to everyone in advance!

 

[netsysadmin]

What email server are you running? If you send an email to a RR address you will most likely also have the same issue as AOL. They block mail from IP adresses deemed as dynamic.

What I do with my Exchange server to fix that is use smarthost setting to route the mail through my RR's smtp server. This way I have no issues of where the email originates from.

John

 

[TiziteLayinLow]

I am currently using MailEnable becuase it is much cheaper.

I am going to be switching to linux based - postfix, courier, spamassasin

Thanks for the advice - I might try to do that with exchange just to get more familiar with exchange as most companies use it and SBS 2003 comes with 75 CALs for it, correct?

 

[ch2]

Originally posted by: TiziteLayinLow
@matt.com email goes out.. goes to IP.. goes back to domain.. gets matt.com (say I set this with RR)..

then @andy.com email goes out.. goes to IP.. goes back to domain.. gets matt.com and says SPAM.. lol

No. It doesn't work like that. As far as PTR's go, all that matters is that your mailserver's canonical name match the result of the PTR lookup. The MTA will use its canonical name no matter what domain it's currently sending email for and no matter what other CNAME or A records point to it. So if mail.domain.com is also sending mail for domain2.com and domain3.com, it will still identify itself to other MTA's as mail.domain.com, and that's OK.

I'm not sure what you were reading, but there really isn't any kind of mailserver to from-address matching in standard SMTP. Perhaps you were looking at something about SPF, which does examine DNS records to do that kind of matching. But there's no problem with SPF and multiple domains - just make sure that each domain's DNS records have an SPF record indicating the canonical name of the server.

 

[spikespiegal]

They block mail from IP adresses deemed as dynamic

If I were to turn on reverse look-up filtering on my mail servers we'd lose correspondence with 1/3 of the companies we do business with 😀

Reverse DNS look-up is dead and buried - the horse is actually dead and the corpse is starting to rot. Too many goober admins out there sending out mail through some random IP on their firewall because they have no clue how to configure it.

Most of my crap mail filtered through my spam server seems to be spoofing dynamic DNS entries anyways, so even the zombie boxes are getting smart.

 

[cleverhandle]

<-- ch2 above, due to a forum snafu...

Originally posted by: spikespiegal
If I were to turn on reverse look-up filtering on my mail servers we'd lose correspondence with 1/3 of the companies we do business with 😀

Reverse DNS look-up is dead and buried - the horse is actually dead and the corpse is starting to rot. Too many goober admins out there sending out mail through some random IP on their firewall because they have no clue how to configure it.

True, but that's still no excuse for not doing it right yourself.

Also, somewhere along the line the ideas of "dynamic address checking" and "reverse lookup matching" seem to have gotten mixed up in this thread. They're totally different things. You could have an IP in a "business" IP block that won't trigger a blacklist, but if you don't have a proper reverse lookup your mail might not go through anyway. And you could (if the ISP allows it) have proper reverse lookup on a "residential" IP block and your mail would still get blocked - dynamic IP blocking doesn't actually do a PTR lookup to make its decisions. It just works off a big table of numeric IP's.