While many an admin can probably work for years without having to look at an SMTP log or network trace, they wouldn’t be email admins. As email admins sharpen their troubleshooting skills, learning the standard SMTP codes that are a part of every data exchange between servers will not only make parsing logs faster, it can help resolve issues with something as basic as a network trace.

The current RFC for the SMTP protocol is 5321. It defines all of the protocol exchanges between servers, and assigns a numeric response code to each. While vendors might implement their own text responses for a particular purpose, the numeric codes will be consistent across platforms.

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