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I am running a WHMCS hosting system for a small number of private clients. For a few of them they never seem to receive the invoice emails I send out. I have ran the emails through a number of tests such as sending one to check-auth@verifier.port25.com and when I get the report back it says:

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Summary of Results

SPF check: pass

DomainKeys check: neutral

DKIM check: pass

Sender-ID check: pass

SpamAssassin check: ham

Yet like I said some clients still never receive their messages while others get them with no problems. If I send them a direct email from my personal account they get it just fine. Most often it is Google Apps users that never even see the email go to their spam folder. The email just never arrives...

Any idea of what else I should check to see if there are any problems that might be making my invoices dissapear?

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    When sending emails to those domains, does your email server log an SMTP 250 response? If so, then you will need to work with the receiving domain to see why it's disappearing. – EEAA Dec 23 '14 at 20:09
  • >SpamAssassin check: ham ??? – Arthur Dec 23 '14 at 20:32
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    @Arthur Ham means good email. As in "it's not spam, it's ham". – Reaces Dec 23 '14 at 20:58
  • Ahhh makes sense. that's actually hilarious. Thanks @Reaces – Arthur Dec 24 '14 at 13:08
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No one other then the recipients mail provider can definitively answer this question for you.

The typical way of handling the problem would be to find the details of the connection from your log server and ensure that the recipients mail server accepted the email. Then call up the recipients mail provider and and ask them what is going on - or if the recipients mail provider is "too big to talk to", I just send it to the recepient and say here is evidence we delivered it and your provider accepted delivery, please talk to them or get them to contact me.

If "regular" email is getting through to your clients you might want to see if you can identify anything in the headers which you are being penalized for - if you can somehow correct the things you can find you might find it lifts your overall mail score enough to get your invoices through.

You may find that restructuring your invoices so that they have more text and less attachment (or maybe replace the PDF with HTML if thats an option) might get you a bit further - but ultimately it sounds like its your clients problem.

One thing I did note is conspicuously absent from the checks you pointed out is any check of reverse DNS. One of the queues many mail servers use is to check that forward and reverse DNS match - is that the case for you. Also, assuming you are a "small player", you might get some traction by reconfiguring your SMTP mail server to relay through your provider - as they handle larger volumes they may be seen as "more credible" for some providers, particularly with respect of things like "Senderbase" scores - which many big providers key off.

  • Reverse DNS may also mean "the envelope sender address is resolvable" - often systems will (by default) send "from" their own hostname, and if it doesn't have a public DNS record it can rejected as a result. – Andrew Dec 24 '14 at 5:15
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If the mail isn't getting delivered to the clients you should be getting bounce messages. Your email server log should give you some hints as too what is happening. In most cases, it should show the message being delivered to their mail server.

If their server is receiving the email, then the problem would be on their end. Try to contact their administrator.

Some servers don't reliably send bounce messages. Unfortunately, many servers accept messages and then determine if they will deliver the message. As a result it is highly probable that a bounce message will be back-scatter spam rather than an appropriate notification.

You may want to check if your server is listed on any blacklists.

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