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We currently have 6+ web application servers all doing direct delivery from IIS ( SMTP service ).

Every couple of months we have to clear ourselves from block lists and having no visibility of emails getting set is a pain.

Whilst googling I found some organisations that supply a mail forwarding / relay service see:

  • SMTP.com
  • www.AuthSMTP.com
  • www.jangosmtp.com

Does any one have any experiance of using a mail server to send messages that is outside their hosting environment.

My convern is that over time we have had to set up sticky addresses to our servers, reverse DNS etc. to get mail to work therefore what what would we need to do to get emails accepted by clients using an external mail server?

I guess what I'm asking is how would the recipients mail server know to trust the email connection though the hosted service when it originated from our data centre?

Many thanks, Jason

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migrated from stackoverflow.com Aug 13 '10 at 15:08

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closed as too localized by Mark Henderson Jan 15 '12 at 5:37

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Well, one mechanism is SPF. You should really do some research in this field - there's a plethora of tutorials on the subject. Also, you might get better help on Server Fault, since this isn't really programming related. sv.wikipedia.org/wiki/Sender_Policy_Framework –  bzlm Aug 13 '10 at 13:03
    
I'm not sure what you're asking exactly. Could you rephrase that last paragraph, please? –  Martijn Heemels Aug 13 '10 at 15:19
    
If you are getting blacklisted every couple of months, you might want to figure out why you are being blacklisted instead of trying to use another server. Odds are the same issue will continue to happen. –  Zypher Aug 13 '10 at 15:55
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2 Answers

It might be a good idea to make sure you send all your outgoing email through another service, that way you don't have to focus on managing an email system also.

But if your problem is that your users thinks that you are sending them spam and reports your emails to various blacklists, then I think that you might need to look over what you really send out, and improve your user experience.

Another thing that might be the reason to why are constantly added to various blacklists are that your servers are hacked, and you are constantly sending out spam below your radar. Blocking outgoing connections to other email servers in your firewall and only allow mails to be routed through your email sender is a good way to make sure that doesn't happen.

Regarding your question on how the email server can trust the emails that comes from you, the SMTP protocol have support for authentication, and you can tunnel it through ssl, so that can be totally secure.

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The recipient mailserver doesn't usually see which computer originated the message. It checks which server is trying to deliver it. So, if your server is blacklisted you can still send mail via a 3rd party server, that you pay for that service.

A good 3rd party SMTP relay would make sure they're not in any decent blacklists, and that they sign any relayed mail via DKIM. Ideally they would take care of whitelisting, ISP throttling, reverse DNS, feedback loops, content scanning, and delivery monitoring. But they can only do so much, if people or filters are marking your mails as spam.

You should setup SPF (and designate the 3rd party servers as allowed senders in SPF). There should be info about SPF available from the 3rd party documentation. Furthermore you should make sure that the mails you only send email to people that have opted-in to your mails, otherwise they will mark it as spam. Some will mark it anyway, just because they forgot they signed up.

Provide a clear footer in the mails that mentions that you're sending the mail because they opted-in for such-and-such, and provide a clear opt-out link in the footer (that actually works, within say 24hrs). Also have an opt-out link and privacy policy on the homepage of your website.

Which 3rd party SMTP server should you use? I can't answer that, but it might be worth looking at Postmark. They have pay-as-you-go pricing, but more importantly they have an interface that allows you to track and correct delivery problems as they happen. You can use SMTP to send a batch, but their API allows you to do much more advanced error handling. Very nice service.

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