1. Paubox Email Suite
  2. Paubox Email Suite: FAQ

Why did an email bounce back saying "Undelivered Mail Returned to Sender" from "Mail Delivery System"?

When you send out an email and it is returned to you, the email message is consider to be a bounceback message. Typically, these returned messages will let you know why the sent email failed. Some bounceback error messages are easier to understand than others.

Below are some common reasons as to why you got a bounceback message.

Common Bounceback Message

    • Inbox is Full: This is a typical indication that the email recipient's inbox is full and cannot accept any more messages. There is little you can do to resolve this error message unless you have another means of contacting that person to notify them of the full inbox. They should usually be able to resolve this issue by deleting old emails or raising their current mailbox quota.
    • Email Account does not exist: If you send an email and get this message, it's best to double check that you have spelled the recipient's email address correctly. If you are sure that is is correct, the email account may have been deleted. If you have another means of contacting the recipients you may try notifying them of the error.
    • IP Address Blacklisted/ Blocked: The bounce back message will typically refer to an IP address being blocked and will usually provide a url with more information as well. We ask that these types of bounce back messages be forwarded to Paubox so that our support team can assist you in resolving this matter. You can submit the error message by emailing support@paubox.com.
    • Greylisting/ Email Message Deferred: Typical messages due to greylisting will usually refer to an email message being "deferred." Greylisting is a methodology utilized by some mail servers to deter spam. If you send a message to a server that uses greylisting and you are not on that server's whitelist the receiving server will "temporarily reject" that message and will often return a message that is formatted very similar to a bounce back but will list the error as temporary instead of permanent. The sending server will attempt to resend the message at a later time, but the recipient will experience a delay in receiving the message. The best way to avoid greylisting is to ask anyone who uses greylisting on their server to add you to their whitelist so they can receive messages from you without delay.
    • Send Limit Exceeded: The maximum email size that can be sent using Paubox is 50MB. However, if you compose a message in HTML, and you have large attachments, your emails can reach over 50 MB. With this type of error it is best to send email and the attachment separately if possible.

If you are still having trouble resolving your outbound email issues. Please contact any one of our customer success managers, and they would be more than happy to help you out.