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When I check any of mailbox from my server with a tool like this one: https://www.port25.com/support/authentication-center/email-verification/ I get:

SPF check:          pass
DomainKeys check:   neutral
DKIM check:         pass
DKIM check:         pass
Sender-ID check:    pass
SpamAssassin check: ham

Seems OK.

My server IP is not blacklisted - I've checked it here: http://mxtoolbox.com/blacklists.aspx

All users in total do not send more than 50 emails a day. They're not spammers, just regular small business users.

Yet still there are problems with e-mail delivery to corporate addresses. Especially when I create a new domain, almost all e-mails from it will end up in spam. Or even worse: they are deleted without notice to sender or recipient.

Popular services like Gmail do not treat them as spam - problem is only with various corporate recipients.

What else should I check or do to put things right?

Marek
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    Here's a few other places you can check with by sending a test email to mailtest@unlocktheinbox.com, sa-test@sendmail.net, dkim-test@altn.com, check-auth@verifier.port25.com, autorespond+dkim@dk.elandsys.com, dktest@exhalus.net, nelson-sbl-test@crynwr.com – Henry Aug 23 '15 at 21:07
  • Also popular email servers have their internal blacklists - you might be on one of those - they won't show up on public blacklist testers. – Henry Aug 23 '15 at 21:08

1 Answers1

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eMail servers will drop your emails on corporate servers even without routing them to spam folders if you don't have correct reverse DNS record. Forward resolved IP should match reverse lookup for a email server responsible for all your domains(basically it is MX DNS record in your domains that point to your email server).

Just for example:

dig +short mail-lb0-f174.google.com a

returned IP : 209.85.217.174

nslookup 209.85.217.174

Returned PTR: 174.217.85.209.in-addr.arpa name = mail-lb0-f174.google.com

So, it match : DomainName <=> IP

You should send your email only through MX server that should be authorized for sending domains and match their SPF records. Probably you already have, but just in case, - email server should run only via static IP.

Usually corporate servers reply with rejection reason. Check your email logs, what error(s) numbers are they returned ?

Alex
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  • The forward and reverse DNS should match the server, not the sending domain, otherwise you couldn't host more than one domain on one IP address. But this is a likely reason though, PTR record not present. – Paul Jul 26 '15 at 23:07
  • Tnx @Paul, I edited my answer with clarification details which exact domain must have forward and reverse record set - it is email server(aka MTA) only need this. – Alex Jul 26 '15 at 23:32
  • Thanks, but revDNS was the very first thing made when setting up this server and it's configured correctly. – Marek Jul 27 '15 at 22:57
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    Try to find IT contacts of those corporations and ask them to send their logs with your IP to find out rejection reason. That is usual practice not only in small business but it works even with big fish. Ask your users to not send the same msg as bulk to multiple recipients, most postmasters rise DCC flag very high since it catching a lot spam. (if it is a case ask then to white-list you). – Alex Jul 28 '15 at 12:05
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    You said it happens when you just created new domain, are you waiting at least 72 hours before using them after creation? SPF record in DNS need time for propagation. May be remote servers didn't catch it yet and see your new domain(s) as a host without SPF record at all. – Alex Jul 28 '15 at 12:05