Unfortunately, different servers sometimes use these codes in a different way, making the whole thing even more complicated… Anyhow, the most critical series of error messages is the 5xx one, and especially the ones from 550 to 559. The first one defines whether the server has accepted the command, fulfilled an action, run into a temporary issue, encountered an error etc the second and the third one refine the description further, stating if there’s been a syntactic problem, or a connection trouble etc. Secondly: any code consist of three digits, and each conveys a particular information. Sometimes it’s just a response containing a detail about the server or an answer to a command.
What does these numbers mean?įirst of all: not any reply code is an error. The problem is that it will generally be very cryptic, like “550 Requested action not taken: mailbox unavailable” or “421 Try again later”. Sometimes your SMTP server may return a particular error message.