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I have been struggling for this issue for months. I have a website, that the registration requires email authentication. I did a check (daily), the statistics are quite interesting. Everyday, out of 300++ users sign up, only 50 - 60 % are activated. There is one time, when my website traffic suddenly burst up, I have around 1000++ users signup per day, and it last about 1 week. However, the statistics still show that only 50 - 60% users are activated. I dont think its a coincidence, since the statistics always shows 50 - 60% users are activated. (I check my database everyday)

I guess, maybe my emails were treated as spams, and thus not able to reach the recipients. But I wonder, how many emails does FaceBook send per day? For me, I received about 20 - 30 emails from them everyday. We all know that, facebook has millions of users, I cant imagine how many emails were sent per day. Those mails are not considered spams?

Is my hosting company responsible for this? or its my script/programming problems?

Here is my server information: OS: Windows Web Server: IIS 6 Web Languages: HTML, PHP, JS + Jquery Mail Server: MailEnable Standard SQL: MySQL 5.XX

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You're actually asking quite a lot of questions and I think you should read up on basic email mechanics first regarding how delivery happens, what current anti-spam measures are, etc. However, I guess this would be out of of scope for SF. – Theuni Dec 9 '12 at 12:10

Did you read Jeff Atwood's - So You'd Like to Send Some Email (Through Code) ?

If you are willing to pay money to avoid the hassle of setting up domain keys, reverse ptr record, sender id, etc., use a third party mail provider like SendGrid.

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Have you looked in your mail logs? I am not familiar with the mail server that you are using, but there must be a log. Does it say anything about dropped emails?

Also, have you setup Reverse DNS on your server? Many email providers will drop you email if you do not have a reverse pointer. This will allow other sites to resolve your IP-address into your domain, Thus you get more reliable. You might have to contact your ISP to setup this.

Reverse DNS on wikipedia

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If there are any issues at your end, this Email Server test could tell you.

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If you search for 'IIS6 SMTP log' you will find information on logging. However your ISP will not send you a complete log if it contains other customers info. I asked my ISP to select out my info from the log but they did not send me anything.

Have you got something like 'recaptca' on the website so as to be sure that it is real people signing up? If not maybe there is some automated attempt going on to try to sign up with false email addresses?

Consider SPF records.

You might also want to consider also offering Open-ID similar to this website.

Perhaps there is some crowd source service somewhere which could be used as a test so that people from various places attempt to sign up and report back results to you.

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Make sure that your server's ip doesn't have a blacklisted ip, apart from the rDNS.

To check that i like MXToolBox.

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The first thing to check is the MX record for the destination domain where you are sending the emails. It must point to the destination mail server. Secondly, check the logs at the destination mail server, they will displace the case why they are not sent to the mailbox.

You may test your mail server by providing the IP Address at the link below:-

It will check the mail server for Open Relay. It will check the mail server for Reverse DNS.

Also, you may check against the Blacklist at the same site.

In case case it all succeeds, check the mail logs at the destination server.

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The question is actually pretty broadly formed and your answer is pretty specific towards issues that we can't be sure are relevant. I'd actually downvote the question. I also suggest giving a little more context for the specific mechanics you mention. – Theuni Dec 9 '12 at 12:09

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