Troubleshooting Missing Emails, Bounceback Messages, and Email Delays


What are potential reasons for various email sending and receiving problems including



Missing Email

In most cases, emails are delivered as intended to the recipient. When email is not delivered, the sender should receive a bounce-back message stating the reason a message was not delivered. While Virginia Tech sends bounce-back messages for anything we block, other email providers may choose not to present them to the sender. Be aware that Virginia Tech discards hostile traffic and some severely misconfigured or seemingly malicious messages without notification.

If the sender didn't receive a bounce-back message, then their email may have been delivered to you, but marked as spam. If you have a Virginia Tech Gmail or Exchange Online account, then you should check your Spam folder and your Trash folder to make sure the email was not marked as spam. If you find the missing email in your spam folder, then you can train the system to not classify the email as spam in the future by following these steps: Stopping Email from Going to Spam.

If you do not receive an email from an automated notification email system (e.g., a password request email or receipt of purchase), then you should contact the IT support group or business group affiliated with that automated email system and request a confirmation as to whether the email was sent and whether any errors occurred. You can ask those other groups for confirmations in the form of SMTP (Simple Mail Transfer Protocol) logs with queue IDs because these confirm the message left their mail system. Note, we cannot use logs from applications or tools as the sender's application log only confirms that they handed the message to their local mail system, if that.

If you didn't find an email in your Spam/Trash folder, the sender of the email didn't receive a bounce-back, and the email wasn't from an automated system, then there is possibly an email delay.

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Bounce-Back Messages

If you send an email to an address and receive a response that states an email could not be delivered, it should contain a bounce-back message that indicates the reason your email was rejected:

Bounce-back Message Reason for Rejection Solution

** Message blocked **

Your message to has been blocked. See technical details below for more information. Learn more here: The response was: Message rejected. See for more information.

Google flagged  the message as spam Google's algorithm flagged the message as spam. Please see Reducing the Spam Score of an Email Message for tips on how to avoid triggering Google from flagging your message.
550- This domain is Blacklisted, Consult Your Postmaster Error Blocked email

See 550 Domain Error when Sending Email to VT Google Workspace for Education Mail Account.

Note that even if you are part of a legitimate organization that is sending well-formed emails, your email provider may have clustered your outbound traffic with that of other organizations or individuals that are sending undesirable messages. In such cases, you should either change email providers or send a request to your current email provider requesting that your email originate from a separate IP, as we may be unwilling to lift the block.

550 5.5.0 Mail Denied, contact your postmaster - generic space Generic sending domain

The sender that receives this message must contact their network administrator or network service provider and request that they update the appropriate rDNS (reverse Domain Name System) record.

By operational policy, we block all generic, user, and customer subdomains as they come to your attention. This is one of the most effective anti-spam techniques we have.[XXXX:XXX:XXX:XXXX:X:XXX:XXXX:XXXXX]:XX: Network is unreachable

Partially configured IPv6 The sender that receives this message must contact their email or network service provider to fix the partial IPv6 configuration.

550 5.1.1 <>... User unknown

In Exchange:
Remote Server returned '550 5.1.1 RESOLVER.ADR.RecipNotFound; not found'

User doesn't exist

You have entered an email address that doesn't exist. Verify that you entered the email address correctly and check with the person that provided the address that it's correct.

If the bounce-back message you received isn't listed here or is unclear, you should try typing that message into a search engine to better understand the cause of the rejection.

When reporting an issue, please send the entire bounce-back message, including headers.

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Email Delays

Though email appears to be sent and received in real-time, this is only the case when systems are performing optimally. Email delays typically occur when system performance is degraded (either due to spammers infiltrating institutional email systems by means of a successful phishing email or an external flood of incoming messages). It is reasonable to expect up to an hour delay for an email to be delivered, and if there are large-scale email delays, they will be posted in the IT Status area on the 4Help portal.

If you have multiple cases within a time frame of a couple days during which email from a specific email address is being delayed more than 45 minutes, then you should collect the delayed email headers. Email headers must be collected by the recipient of the delayed email. You should not submit headers collected from emails from the sender's outbox as they lack the required information.

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Retrieving and Submitting Email Headers

When submitting headers to 4Help, do so by copying and pasting the full header into your incident or message. Please do not submit headers as attachments or in the form of PDF or Word documents.

The recipient's email messages are the ones for which you want to collect headers. Do not submit headers from a sender's copy of an email message.

Retrieve Header from Email in Outlook Web App (OWA)

  1. Open the message.
  2. Click the three dots (ellipsis) at the topsright of the message.
  3. Click View.
  4. Click View Message Details.
  5. Copy and paste the entire content in the window into your 4Help ticket.

Retrieve Header from Email in Outlook Desktop

  1. Open the message.
  2. Click File.
  3. Click Properties.
  4. Copy and paste the entire content in the Internet Headers section into your 4Help ticket.

Retrieve Header from Email in Gmail

  1. Open the message.
  2. Click the three dots (ellipsis) at the top-right of the message.
  3. Click Show original.
  4. Click Copy to Clipboard.
  5. Paste the copied content into your 4Help ticket.

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