Mail is not being received by some recipients sometimes and we receive no failure message

25 pts.
Greetings, we have a single mail domain with two mail hosting providers and two ISPs. We set it up this way so that if an ISP or Mail provider has issues we can fail over to the other. We use a sonicwall for this function. Users have OE6 clients with two accounts configured with the same email address but different smtp & pop settings. Occasionally we send mail out and it is not received but we get no failure notice. If the user switches to the other account and sends to the same recipient they may receive it fine. At first we thought we were going into a spam bucket on the recipients end but other users here can send to the same recipients fine while others experience the lost mail issue. We additionally discovered that mail sent through the web based user accounts that fail from the clients go through fine. Any thoughts?

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Check the Reverse DNS of the public IPs used in both ISPs to send email. If the IP does not resolve to the DNS record of the server then the email will be listed as spam by most mail servers. If this is the case then contact the ISP to include a PRT record. Another problem could be that the IP used to send email from is blacklisted, there are multiple inline tools to check is this is the case too. And my favorite one…make sure you ISP is not blocking TCP port 25.

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  • TomLiotta
    Is it predictable? I.e., if the same users do similar steps the next day for the same recipients, can you successfully predict that they will fail? Or does it shift from user to user, recipient to recipient? Tom
    125,585 pointsBadges:
  • Iseriestek
    Not predictable - it appears to effect the same recipients but is intermittent. We have 50 or so users and a handful report the problem but that does not mean that more are experiencing the issue and are not reporting it. We also do not know if other recipients are experiencing the same thing (we only know the recipients because they are expecting mail and report when it is not received). I also noticed that the users contacts were created prior to the second mail provider being added. If we switch accounts manually in the email and send from the second account it appears that the mail goes through. It is quite confusing since the mail goes through using either account sometimes.
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