Email Reasons
Error 403 - You are not authorized to send from that email address
Possible Causes
There is an issue with the sender’s email address.
Possible Solutions
Please contact Shepherd support for assistance.
Error 421 - Message from (X.X.X.X) temporarily deferred
Possible Causes
This message was temporarily delayed due to high-volume traffic.
Possible Solutions
The system will attempt to resend the message for up to 72 hours.
Error 450 - Too frequent connects from 198.37.147.135, please try again later
Possible Causes
The recipient’s mailbox was unavailable, typically because it was locked or not routable at the time.
Possible Solutions
The system will attempt to resend the message for up to 72 hours.
Error 451 - Authentication failed: Maximum credits exceeded
Possible Causes
This message was unable to send due to a credit limit.
Possible Solutions
Please contact Shepherd support for assistance.
Error 452 - Too many recipients received this hour (throttled)
Possible Causes
This message was temporarily delayed due to insufficient system storage.
Possible Solutions
The system will attempt to resend the message for up to 72 hours.
Error 550 - Requested action not taken: mailbox unavailable
Possible Causes
This message failed to send because the recipient’s mailbox was unavailable.
Possible Solutions
We recommend verifying the email address is spelled correctly.
Error 551 - User does not exist
Possible Causes
This message failed to send because the recipient’s mailbox does not exist.
Possible Solutions
We recommend requesting another email address from the client.
Error 552 - This message is larger than the current system limit or the recipient’s mailbox is full. Create a shorter message body or remove attachments and try sending it again
Possible Causes
This message failed to send because the recipient’s mailbox is full.
Possible Solutions
We recommend requesting another email address from the client.
Error 553 - Invalid/inactive user
Possible Causes
This message failed to send because the mailbox is malformed or does not exist.
Possible Solutions
We recommend requesting another email address from the client.
Error 554 - ERROR: Mail refused
Possible Causes
This message failed to send due to technical issues.
Possible Solutions
We recommend verifying the email address is spelled correctly.
Error 'Other' - Delayed Bounce - Unable to Parse Server Reason
Possible Causes
This message failed to send with no reason from the recipient.
Possible Solutions
We recommend verifying the email address is spelled correctly.
SMS Reasons
For further explanations on SMS error messages, search the error code here by using the search bar located on the top right.