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Editorial Team
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Asked: 2026-05-23T20:26:39+00:00

I work at a university, on a project for a web driven academic management

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I work at a university, on a project for a web driven academic management system and I’m currently facing the following problem:

Sometimes the application needs to send e-mails, most of then are sent on demand (users ask for a password recovery link, for example). Many emails for this kind of service are sent daily, and if on a peak of access they are sent massively. This has caused our email server to be included in blacklists of common email providers (like yahoo and hotmail), resulting in failures on email delivery.

What are the common causes for this kind of problem? Is it possible to avoid these blacklists? Or at least is there any good practices to follow so I can “flag” these useful emails as non-spam or safe email?

thanks for reading.

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  1. Editorial Team

    first of all, check if those messages are really sent to email addresses in your account database. maybe there is a security hole in your application that allows sending messages to arbitrary recipients. an indicator of that would be if your domain or ip is blacklisted not only at specific providers like yahoo or hotmail, but also on public blacklists like spamhaus.
    (“most of then are sent on demand”.. makes me think.. what about the others? could they be interpreted as spam by many recipients?)

    then you need to find out if your server is blocked due to
    the amount of messages sent or due to the content looking “spammy”.

    Check your logs from the time before the blacklisting happens. Do you see many deferred messages (4xx error code), do they contain error messages that indicate too many messages from your IP?
    if so, configure your MTA to throttle message delivery to those providers.

    also check your mailserver setup:

    • correct fully qualified HELO?
    • matching reverse dns?
    • If you have DKIM , SPF and the like… are the settings correct?

    finally, examine the generated messages. Do they have all required headers? Run them through spamassassin and check the result. adapt the formatting of your messages accordingly.

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