Troubleshoot common email delivery errors when a reply fails to send from the SparrowDesk Inbox.
When you send an email reply from the SparrowDesk Inbox, the message may occasionally fail to deliver. This usually happens because the recipient’s email address, mailbox, or email provider rejected the message.
When this happens, SparrowDesk shows a delivery failure note inside the conversation. The note helps your team understand which email address could not receive the reply and why the delivery failed.
In most cases, these errors come from the customer’s email provider. For example, the customer’s mailbox may be full, the email address may no longer exist, or their mail server may have blocked the message.
You can try sending the reply again later, contact the customer through another email address, or use another available channel.
Delivery failure notes do not reopen closed conversations automatically.
Here are some common email delivery errors and what they usually mean.
Error code | What it means | What you can do |
|---|---|---|
421-4.7.28 | The recipient’s provider temporarily deferred the email. This can happen when the provider detects unusual sending activity or rate limits messages from a domain. | Try sending again later. Make sure your sending domain is properly authenticated with SPF and DKIM. |
550 | A general delivery failure. This can mean the email address does not exist, the message was blocked, the mailbox is full, or the recipient’s provider rejected the email. | Check the full error message for more details. Verify the customer’s email address and try another contact method if available. |
550-5.1.1 | The email address is invalid or no longer exists. It may also happen if there is a typo in the customer’s email address. | Confirm the customer’s email address and update the contact before sending again. |
550-5.7.1 | The message was rejected because of a security, spam, authentication, or policy rule on the recipient’s side. | Check that your sending domain is authenticated. Ask the customer to check whether their email provider or IT team is blocking your messages. |
552-5.2.2 | The recipient’s mailbox is full and cannot receive new messages. | Try again later or contact the customer through another channel. |
554-5.4.4 | The recipient’s mail server could not route or deliver the email. This may be caused by DNS issues, server configuration, or network restrictions. | Try again later. If the issue continues, ask the customer to check their mail server settings. |
554-5.4.7 | The message could not be delivered after repeated attempts. This may be caused by routing issues, temporary server problems, or provider restrictions. | Try again later or use another email address/channel if available. |
If a customer marks one of your emails as spam, future emails to that address may be blocked to protect sending reputation.
In this case, replies from SparrowDesk may fail even if the customer’s mailbox is active. The error message may not always clearly say that the customer marked the message as spam.
To continue the conversation, confirm with the customer through another channel and ask them to allow emails from your support address.
If an email address repeatedly fails with a permanent delivery error, it may be added to a bounce or suppression list. This prevents future emails from being sent to that address and helps protect your email sending reputation.
Before requesting removal from a bounce list, make sure the original issue has been fixed. For example:
If you believe the address is valid and the issue has been resolved, contact SparrowDesk support for help.
If you see a message failed error inside the Inbox, first try sending the message again.
If the error continues:
If the issue still isn’t resolved, contact SparrowDesk support with the conversation link and the error message shown in the Inbox.
To improve email deliverability from SparrowDesk:
If delivery failures continue, reach out to SparrowDesk support with:
This helps the support team investigate the issue faster.
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