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## 6 Debugging

Sometimes delivery fails, often with the generic error message ‘`Sending failed; SMTP protocol error`’. Enabling one or both of the following variables and inspecting a trace buffer will often give clues to the reason for the error.

`smtpmail-debug-info`
  The variable `smtpmail-debug-info` controls whether to print the SMTP protocol exchange in the minibuffer, and retain the entire exchange in a buffer ‘`*trace of SMTP session to server*`’, where server is the name of the mail server to which you send mail.
`smtpmail-debug-verb`
  The variable `smtpmail-debug-verb` controls whether to send the `VERB` token to the server. The `VERB` server instructs the server to be more verbose, and often also to attempt final delivery while your SMTP session is still running. It is usually only useful together with `smtpmail-debug-info`. Note that this may cause mail delivery to take considerable time if the final destination cannot accept mail.