Nearly everyone has experienced the frustration of sending an email, only to later learn that the recipient never received the message. Unfortunately, spam filter false-positives are not uncommon. As a result, it is not uncommon for legitimate messages to be erroneously filtered by spam filters. In these cases, the message might be routed to the recipient's junk or spam folder, or the message may be silently discarded altogether.

Spam filter false-positives can occur for a number of reasons, including: a sending SMTP mail server is not properly configured or does not follow standard best practices for email, the sender's lack of use of message authentication, or poor mail server IP reputation (blacklisting or greylisting).

What we do to maximize the likelihood of messages being successfully delivered to their recipients:

• We apply standard best practices for email
  Configuring email servers correctly is not trivial. If the server's DNS is not setup correctly, or the server does not identify itself correctly to receiving MX's, mail sent from that server is likely to be trapped by spam filters on the receiving end. We know how to get it right.
  
  
• We employ message authentication methods
  Message authentication methods, such as SPF and DKIM, are used to help spam filters recognize your outgoing messages as legitimate messages, and not spam. We provide you with the necessary information to setup an SPF record for your domain, and all messages sent through UltraSMTP are DKIM-signed using your keys or ours.
  
  
• We don't operate a free email service, and we don't provide mass-emailing services
  Free email services and mass-emailing services attract spammers. Spammers send spam, then the service's IP addresses get blacklisted. Then, legitimate mail sent from the service's IP addresses gets trapped by spam filters. We don't want that. We don't provide free email service or bulk email services, so that the services that we do provide to our paying clients are of utmost reliability. Moreover, our plans are intentionally structured to be cost-effective for typical business or personal use, or for sending a moderate volume of automated transactional emails - but cost-prohibitive for spamming. Simple economics keeps spammers from using our services, which makes our services more reliable for our paying clients.
  
  
• Blacklist Monitoring
  Because UltraSMTP's mail servers are not used for sending bulk mail or junk mail, our mail servers rarely get blacklisted, and therefore mail sent through our mail servers is less likely to be trapped by spam filters. In addition, we routinely monitor the blacklists used by spam filters. In the event that any of our mail server IP addresses are blacklisted, we immediately address the problem with the blacklist administrator to rectify the problem, and we address the problem with the sender to ensure that it never happens again.
  
  
• Greylist Management
  Many receiving mail servers will routinely reject a message initially from a sending mail server as a means for controlling spam. In order to deliver the message, the sending mail server may have to make several retry attempts. UltraSMTP will automatically re-attempt to deliver deferred messages until they are accepted by the receiving mail server.
  
  
• Feedback Loop (FBL)
  Feedback Loop (FBL) is a standard that is used to alert the sending party when an email is determined to be spam at the receiving end. We are registered for feedback loop service with most of the major email service providers, so that in the event that an email sent through UltraSMTP is marked as spam, we are notified, so that we can take appropriate action.
  
  

Notwithstanding all of the above, SMTP email is inherently less than 100% reliable. In spite of all of the above measures, it is possible that a message sent through UltraSMTP (or any SMTP server) can go unreceived by the recipient. To mitigate this inherent problem, UltraSMTP offers a comprehensive set of tools for tracking and confirming delivery of messages after they've been sent, including Delivery Status Notices, Opened Message Alerts, and Document Delivery Confirmation.


Related:
Blacklists, Greylists, IP Reputation, and Spam Filters
Why do Legitimate (non-spam) Email Messages Sometime Not Reach Their Recipients