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We have a service that requires a registration and the registration process sends some confirmation emails.

These emails say in a three-line message that you have to click some link with a generated token to complete the registration. We send these emails in several languages, always HTML-formatted.

These emails are always delivered instantly to Gmail, Yahoo and Hotmail accounts. It took quite some tweaking though to make our local Exchange server pass them through; the "intelligent" spam filter was always rating these emails as around 75% suspicious. Another mail server located on the same shared hosting sends emails that always get through. At the same time, other confirmation emails sent to our local Exchange server, usually get delivered to our mailboxes. The problem seems to be specific to our confirmation emails only.

The question is how do we make sure that these confirmation emails are not trashed by the spam filters? Is there a safe technique to, e.g. use some specific sender id like 'noreply' or including some specific text into the message, maybe more text or something else to let the spam filter classify the confirmation message as such.

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See also:… – Piskvor Sep 5 '11 at 10:39
possible duplicate of How to send emails and avoid them being classified as spam – mailq Sep 5 '11 at 10:48
up vote 5 down vote accepted

I don't know Exchange, but I am quite sure that you can somewhere configure to trust every mail coming from your own servers.

On a more general note some hints to avoid being classified as spam:

  • Don't send spam (send only requested mails, make it really easy to unsubscribe for newsletters etc., don't give anyone a reason to tag your mails as spam)
  • Try to personalize even the registration confirmation: "Dear John Doe" instead of "Dear Customer".
  • Don't be an open relay
  • Make sure your DNS entries (forward and reverse) are in order
  • Configure DKIM and/or SPF records
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The problem was solved by personalizing the message a bit more, i.e. adding a signature. The Exchange server rates the message as 0% suspicious whenever it sees a signature! – Elijah Saounkine Sep 5 '11 at 11:24

In addition to what SvenW has outlined, also avoid utilizing dynamic Internet IP addresses from the ISP. A fair number of well used black-lists automatically identify dynamically assigned IP blocks as probable spam sources.

Even with a static Internet IP, the address should be verified as not being mis-classified by the ISP - which can lead to the IP block being incorrectly identified as dynamically assigned (back to being listed by the black-lists).

There are also certain hosting outfits that are "spammer friendly" where most of their IP blocks are black-listed as a result. You may factor that in when/if shopping for a hosting provider.

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