Sometimes your Perimeter may return a particular error message. The problem is that it will generally be very cryptic, like “550 Requested action not taken: mailbox unavailable” or “421 Try again later”. What does these numbers mean?
First of all: not any reply code is an error. Sometimes it’s just a response containing a detail about the server or an answer to a command. Secondly: any code consist of three digits, and each conveys a particular information. 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.
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. In particular, you will probably get a lot of 550 SMTP error codes – that is, a problem that concerns the recipient’s email address.
Finally, remember that it’s much easier to deal with these error codes if you choose to rely on a professional SMTP server that will help you solve any issue. Perimeter, for instance, comes with a 24/7 customer support: you can try it free and forget once for all these issues.
And here’s a list of the SMTP error or reply messages that Perimeter will send to you, with an explanation and a tip about what to do:
4XX Error codes
| Error message | Descripción | Resolution |
|---|---|---|
| You can only send xx msgs per xx | The sender has been ratelimited. | Reduce the sending speed, try again after the specified period |
5XX Error codes
| Error message | Descripción | Resolution |
|---|---|---|
| The sender xxx.xxx.xxx.xxx is banned | The sender’s IP address has been added to the banned senders list | The address will need to be removed from the banned senders list |
| The domain example.com is banned | The sender’s domain name has been added to the banned senders list | The address will need to be removed from the banned senders list |
| Dictionary attack detected | The system has detected an attempt to harvest email addresses | Send email to only existing addresses only our update your mailing list |
| Legitimate bounces are never sent to more than one recipient. | The sender’s sent a bounce message to more than one address | |
| Restricted characters in address | The email address contains characters that should not be used | Check the email address |
| Sender verification failed | The senders email address could not be verified | Ensure that the email address you use for sending does accept email |
| Recipient verification failed | The recipient email address could not be verified | Check the email address you are sending to |
| Relay not permitted | The sender is not authorised to send email via the server. | Request the administrator to add the sender to relay settings |
| The email address does not exist | The checks have determined that the email address does not exist | The sender must resend the email to a valid recipient address. |
| The sender is in a black list rbl.baruwa.net | The sender is listed in the rbl.baruwa.net DNS blacklist | This list does not accept removal requests, the address will be removed automatically when the amount of unsolicited email reduces. |
| The sender is in a black list hostkarma.junkemailfilter.com | The sender is listed in the hostkarma.junkemailfilter.com DNS blacklist | The sender should request removal of the associated address via the website – http://ipadmin.junkemailfilter.com/remove.php |
| The sender is in a black list bl.spameatingmonkey.net | The sender is listed in the bl.spameatingmonkey.net DNS blacklist | The sender should request removal of the associated address via the website – http://spameatingmonkey.com/delist.html |
| The sender is in a black list zen.spamhaus.org | The sender is listed in the zen.spamhaus.org DNS blacklist | The sender should request removal of the associated address via the website – http://www.spamhaus.org/lookup/ |
| The sender is in a black list bl.spamcop.net | The sender is listed in the bl.spamcop.net DNS blacklist | The sender should request removal of the associated address via the website – https://www.spamcop.net/bl.shtml |
| The sender is in a black list cbl.abuseat.org | The sender is listed in the cbl.abuseat.org DNS blacklist | The sender should request removal of the associated address via the website – http://cbl.abuseat.org/lookup.cgi |
| The message failed SPF checks | The sender’s is not authorised to send messages for the domain | Check the domain SPF record or send from authorised hosts only. |
| The sender xxx.xxx.xxx.xxx has no reverse DNS record | The sender’s IP address does not have a PTR record | Create a reverse DNS record for the sending IP address |
| Blacklisted file extension detected. | The message contains an executable which should not be sent via email. | Do not send executables via email |
| The message was rejected due to security policies | The message triggered an Anti-Virus Engine signature | Check your computer or the message |
| This message is administratively prohibited | The message was rejected because it contains a subject that is prohibited or contains a blank reply-to header. | Add the sender to Empty Reply Checks Exemptions List |
| The sender did not present a HELO/EHLO greeting | The sender did not present a HELO/EHLO greeting | Configure your client to send a HELO/EHLO message |
| The sender presented HELO as an IP address | The sender used an IP address as the HELO/EHLO message (See RFC2821 4.1.3) | Configure your client not to send an IP address as the HELO/EHLO message |
| DKIM failure: xx | The email failed DKIM checks | Ensure that your DKIM policy is correct and that you are signing all messages |
| Authentication is allowed only once per message | Authentication is allowed only once per message in order to slow down brute force cracking | Ensure that your SMTP authentication credentials are correct |
| The sender is blacklisted due to repeated auth failures | The sender is locally blacklisted for a brute force auth (username+password) cracking attempt | Ensure that your SMTP authentication credentials are correct |