|101||The server is unable to connect|
|111||Connection refused or inability to open an SMTP stream|
|211||System status message or help reply|
|214||A response to the HELP command|
|220||The server is ready|
|221||The server is closing its transmission channel, It can come with side messages like "Goodbye" or "Closing connection"|
|250||Its typical side message is "Requested mail action okay completed": meaning that the server has transmitted a message|
|251||"User not local will forward": the recipient's account is not on the present server, so it will be relayed to another|
|252||The server cannot verify the user, but it will try to deliver the message anyway|
|354||The side message can be very cryptic ("Start mail input end ."), It's the typical response to the DATA command|
|420||"Timeout connection problem": there have been issues during the message transfer|
|421||The service is unavailable due to a connection problem: it may refer to an exceeded limit of simultaneous connections, or a more general temporary problem|
|422||The recipient's mailbox has exceeded its storage limit|
|431||Not enough space on the disk, or an "out of memory" condition due to a file overload|
|432||Typical side-message: "The recipient's Exchange Server incoming mail queue has been stopped"|
|441||The recipient's server is not responding|
|442||The connection was dropped during the transmission|
|446||The maximum hop count was exceeded for the message: an internal loop has occurred|
|447||Your outgoing message timed out because of issues concerning the incoming server|
|449||A routing error|
|450||"Requested action not taken – The user's mailbox is unavailable", The mailbox has been corrupted or placed on an offline server, or your email hasn't been accepted for IP problems or blacklisting|
|451||"Requested action aborted – Local error in processing", Your ISP's server or the server that got a first relay from yours has encountered a connection problem|
|452||Too many emails sent or too many recipients: more in general, a server storage limit exceeded|
|471||An error of your mail server, often due to an issue of the local anti-spam filter|
|500||A syntax error: the server couldn't recognize the command|
|501||Another syntax error, not in the command but in its parameters or arguments|
|502||The command is not implemented|
|503||The server has encountered a bad sequence of commands, or it requires an authentication|
|504||A command parameter is not implemented, Bad email address, Bad email address, A DNS error: the host server for the recipient's domain name cannot be found|
|513||"Address type is incorrect": another problem concerning address misspelling, In few cases, however, it's related to an authentication issue|
|523||The total size of your mailing exceeds the recipient server's limits|
|530||Normally, an authentication problem, But sometimes it's about the recipient's server blacklisting yours, or an invalid email address|
|541||The recipient address rejected your message: normally, it's an error caused by an anti-spam filter|
|550||It usually defines a non-existent email address on the remote side|
|551|| "User not local or invalid address – Relay denied",
Meaning, if both your address and the recipient's are not locally hosted by the server, a relay can be interrupted, 552 "Requested mail actions aborted – Exceeded storage allocation": simply put, the recipient's mailbox has exceeded its limits
|553||"Requested action not taken – Mailbox name invalid", That is, there's an incorrect email address into the recipients line|
|554||This means that the transaction has failed, It's a permanent error and the server will not try to send the message again.|
550 5.1.1 Recipient address rejected: User unknown in virtual alias table
This is the bounce back message that is received by the sender from our server if the destination email address does not exist. The same error message is received if the recipient has a mail loop. That is, if the recipient has set a forward to another email address and that email address is forwarded back to the original one. In this case, you need to remove the loop in order to receive the emails.
If there is a forward set for an account, and an email is sent to that account, if for some reason the forwarded email is not sent, the original sender may get the above error.
For example, firstname.lastname@example.org if forwarded to email@example.com, if a third user firstname.lastname@example.org emails to email@example.com, he may get the above error if the forwarded email is bounced.
550 5.1.1 Protocol error
This error code ideally suggests that the sender has used SMTP protocol instead of ESMTP, thus the outbound mail of the sender was rejected. In short, the sending client doesn't properly communicate and makes errors in the SMTP protocol.
550 5.3.2 Service currently unavailable
The error code 5.3.2 usually means that the system is not accepting network messages. We would thus need to look outside Exchange for a connectivity problem.
The error code ideally occurs ideally for two reasons which are listed below:
554 5.7.1 Service unavailable; Client host X.X.X.X blocked using zen.spamhaus.org
This is the error message that is received of the IP address of the sender is listed at zen.spamhaus.org
For further details, please check http://www.spamhaus.org/zen
OR check http://www.spamhaus.org/query/bl?ip= and contact zen.spamhaus.org to get the IP De-listed.
550 5.7.1 : Helo command rejected: You aren't localhost
550 5.7.1 : Helo command rejected: You aren't localhost.localdomain.
550 5.7.1 : Helo command rejected: You are not me
Our servers do not accept SMTP HELO command as HELO localhost or HELO localhost.localdomain or HELO . We accept HELO from a valid Domain Name or your computer name which is other than your domain name. Please check with your ISP or Mail administrator for this issue.
554 5.7.1 : Relay access denied
There are couple of reasons for this error while sending an email
Please contact support.
551 5.7.1 The message was rejected due to classification as Virus,Spam or high bulk ratio
This is a bounce back message that you receive when an email is classified as spam while sending out. If you feel that a genuine email is rejected as spam, you need to send the same email with the full headers and the content to our support team. That email in question will be reviewed manually.
530 5.7.0 Recipient address rejected: Authentication Required
This error comes when your sending mails to remote domain without using smtp authentication.
550 5.4.5 Recipient address rejected: Hourly domain sending quota exceeded
This is the error message that you get if your domain name exceeds the hourly quota set for the domain name. Here, the term 'hour' refers to the last 60 minutes.
550 5.4.6 Recipient address rejected: Hourly sending quota exceeded
This is the error message that you get if the user (that particular email address) exceeds the hourly quota set. Here, the term 'hour' refers to the last 60 minutes.
553 5.7.1 Sender address rejected: not owned by user firstname.lastname@example.org
This is the error message that is received when you are trying to send an email as a different user.
554 5.7.1 : Recipient address rejected: USER IS SUSPENDED
This error comes if user is suspended in Control Panel.
522 5.7.1 : Recipient address rejected: Requested mail action aborted: exceeded storage allocation
This error comes if the user is overquota.
554 5.7.1 : Sender address rejected: Access denied
This error comes when the sender address is blocked on our server. Generally this is done if spam has originated from this user.
450 4.1.8 : Sender address rejected: Domain not found
Our inbound servers require that the hostname for the sender server should have valid MX or A records in order to accept emails from it. You need to contact the sending server's email admin to add valid DNS records for his server.
450 4.7.1 Client host rejected: cannot find your reverse hostname
Our inbound servers require reverse hostname for the sender server to be present in order to accept the email. You need to contact the reverse hostname's email admin to add the rDNS to into his server.
450 4.7.1 : Recipient address rejected: Policy Rejection- Quota Exceeded
This error comes from our incoming mail server if user is receiving excessive amounts of mails.
450 4.7.1 Recipient address rejected: Access denied
This occurs when the recipient address is invalid. i.e., not in form of user@domainname OR if the Recipient address is blocked on server.
451 4.3.5 Server configuration problem - try again later
451 4.7.1 Service unavailable - try again later;
This error most likely occurs if there is a configration error with our servers. If you encounter any of the above messages, please contact our support with the details.
452 4.5.3 Error: too many recipients
The error message is encountered when the user is exceeding the limit of more than 50 recipients in an email. The list of recipients is inclusive of To,Cc and Bcc. If you encounter the above error, reduce the number of recipients in the email and try again.