Various SMTP Error Codes Explained for Business Emails Print

  • 0

Error : Wrong or missing login data to access mail transport server Please check the associated account's settings/credentials

  • If your email account is not in ACTIVE status (either SUSPENDED or BLACKLISTED) then you will see the above mentioned error message while sending emails from that email account.
  • For a suspended email account, you need to contact the administrator of email dashboard. For a blacklisted email account, you need to contact our Abuse helpdesk.

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, [email protected] if forwarded to [email protected], if a third user [email protected] emails to [email protected], 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:
1). The sending IP is blacklisted at an RBL or blacklist monitoring site. (You may verify the same by inputting the IP via this link: )
2). There is a temporary block on the IP on our Inbound server due to multiple mails from this IP. Feel free to contact our support desk for more information and regarding de-listing the same.
3). If sending IP does not have a reverse PTR record configured. Reference URL:

554 5.7.1 Service unavailable; Client host X.X.X.X blocked using;
This is the error message that is received of the IP address of the sender is listed at
For further details, please check
OR check<your_ipaddress> and contact to get the IP De-listed.

550 5.7.1 <[email protected]>: Helo command rejected: You aren't localhost.
550 5.7.1 <[email protected]>: Helo command rejected: You aren't localhost.localdomain.
550 5.7.1 <[email protected]>: Helo command rejected: You are not me

Our servers do not accept SMTP HELO command as HELO localhost or HELO localhost.localdomain or HELO <your_domain_name>. 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 <[email protected]>: Relay access denied;
There are couple of reasons for this error while sending an email

552 5.3.4 Message size exceeds fixed limit
A 552 email error is typically encountered when there is a problem related to an attachment in your email. Either it has exceeded the size limits of the remote server, or the file-type isn't allowed by the remote server.
1. For file extensions not allowed on our servers, please do refer to the following link:
2. For mail (including attachment) sent across from our servers, we allow clients to send upto 30 MB of data.

Solution: Examine the size of the message including attachments. Try zipping the file content.

551 5.7.1 The message was rejected due to classification as Virus,Spam or high bulk ratio. Please see
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 <[email protected]>Recipient address rejected: Authentication Required.
This error comes when your sending mails to remote domain without using smtp authentication.

550 5.4.5 <[email protected]>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 <[email protected]>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 <[email protected]>Sender address rejected: not owned by user [email protected]
This is the error message that is received when you are trying to send an email as a different user. This error message is seen by the users who are using Exchange servers with our system.

You need to add an identity for the same in the webmail. For example,

554 5.7.1 <[email protected]>: Recipient address rejected: USER IS SUSPENDED 
This error comes if user is suspended in Control Panel.

522 5.7.1 <[email protected]>: Recipient address rejected: Requested mail action aborted: exceeded storage allocation
This error comes if the user is overquota.

554 5.7.1 <[email protected]>: 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 <[email protected]>: 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 sender server IP to be present in order to accept the email. Please ensure that the valid PTR records are added for all outbound server IP's. Post adding the required rDNS records our inbound servers will accept mails from the remote mail hosting server.

450 4.7.1 <[email protected]>: 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 configuration error with our servers. If you encounter any of the above messages, please contact our support helpdesk 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.

Was this answer helpful?

« Back