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Error messages when using SMTP

Last updated February 2020

If you send mail through SMTP rather than REST, there are a few errors that are specific to SparkPost. The list below covers each of them, as well as what to do when you receive them.

For error messages that are not listed below, see one of the popular SMTP reply code guides, like

ResponseWhat it meansHow to correct it
535 5.7.8 Sorry. *** No authentication type succeededThere is some problem with the authentication credentials. API key, user name, etc.Confirm that the API key has the Send via SMTP permission and the user name SMTP_Injection.
550 5.6.0 JSON parsing error in X-MSYS-APIThe X-MSYS-API header is malformed in some wayFix the header's json. The error message usually supplies additional details about the problem. See the API Docs for more information about the format.
550 5.7.1 Unconfigured Sending Domain <>The domain part of the "From" address isn't a configured sending domainUse a "From" address that uses a configured sending domain. See Creating Sending Domains if you need to create a sending domain.
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