Exact Hosting Hostedemail Spam and Rejections Guide

We've made a recent switch from a third-party service to something in-house to address the demand for better spam protection. With the observed benefit of meeting a better spam-free email environment, this change also affords us quicker turnarounds for new features, stability, closer alignment with our acceptable use policy, and better outbound IP protection from external blacklists.

Our development team is hard at work implementing a new feature to the new spam solution to intelligently adjust spam policies based on everyday user interaction with our hostedemail product.

• Troubleshooting guide
• Customers cannot send emails to another user
  • Manually marking an email as spam
  • SMTP reject troubleshooting
  •  
  • Bounceback reject troubleshooting
• Additional troubleshooting

Troubleshooting guide

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Customers cannot send emails to another user

It's important that we distinguish the difference between an SMTP-reject and a bounce-reject.

An SMTP-reject is when the user email client or webmail client produces a notification stating that this message cannot be sent. This means that we are not allowing the message to be sent.

A bounce-reject is when the user sends the email and later discovers a message in their inbox claiming the message was not successfully delivered. This means that the recipient email server rejected the message.

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Manually marking an email as spam

Marking an email as spam reports various elements of the email like the sender, email headers, email contents, etc. to the email server. The spam filter will incorporate these elements and filter out future emails that are similar.

Reporting legitimate marketing emails as spam will be ineffective since they are considered a trusted sender. Unsubscribing from their mailing list will prevent future marketing emails.

Note: Marking an email as not spam will teach the spam filter which kinds of emails are considered safe.

1. Mark the email as Spam.
   
2. Press Accept to confirm the selected email as spam.
   Important: If you confirm to share your data with our Spam partner, the pop-up will go away and you will not be prompted to make a selection going forward. Should you choose to decline, when you mark an email as Spam, the pop-up will appear each time.
   

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SMTP reject troubleshooting

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Bounceback reject troubleshooting

Ask the user for a copy of their auto-generated undelivered mail bounce message. The recipient email server, at its discretion, may or may not provide a reason why the message was rejected. If a reason is provided, attempt to self-serve and correct the problem. 

Common reasons for rejection include:

• The recipient does not exist
• The recipient's mailbox is full
• The sender did not pass SPF, DKIM, DMARC policy check
• Sender's IP is blacklisted
  • For this scenario, advise our support team. Depending on the blacklist, we may be able to have our IP delisted.

Additional troubleshooting

If you are still struggling to determine the reason for message delivery failure, email us at help@exacthosting.com.

For every troubleshooting case scenario, please provide:

• The name of your account
• The recipient's email address
• The sender's email address
• The date, timestamp, and timezone of the failure

Common Error Codes

5.x.x Series (Permanent Failures)

These indicate that the message cannot be delivered as-is and the sender must take corrective action.

• 550 5.1.1 User unknown
  The recipient’s email address doesn’t exist on the receiving mail server.
  Example: Typo in the email address.
• 550 5.4.1 Relay access denied
  The server won’t relay the message because the sender isn’t authenticated or allowed.
• 552 5.2.2 Mailbox full
  The recipient’s mailbox has exceeded its quota.
• 553 5.1.2 Invalid recipient address
  The email address syntax is invalid, or the domain doesn’t exist.
• 554 5.7.1 Message rejected due to content or policy
  Similar to your example — often due to spam filters, blacklisting, or security policies.

4.x.x Series (Temporary Failures)

These suggest a transient issue; the mail server may retry later.

• 421 4.3.2 Service not available
  The receiving server is temporarily down or overloaded.
• 450 4.2.0 Mailbox unavailable
  The recipient’s mailbox is temporarily unavailable (e.g., server maintenance).
• 451 4.3.0 Temporary server error
  Could be due to a spam check, DNS issue, or server resource problem.
• 452 4.2.2 Insufficient system storage
  The receiving server has run out of disk space or resources.

Authentication & Security Errors

These are often tied to modern email security standards.

• 535 5.7.8 Authentication credentials invalid
  Wrong username/password when sending through SMTP.
• 530 5.7.0 Authentication required
  Server requires authentication before allowing mail relay.
• 550 5.7.26 Unauthenticated email from domain is not accepted
  Usually DMARC, SPF, or DKIM authentication failure.
• 554 5.7.9 Message not accepted for policy reasons
  Blocked by DMARC enforcement or spam filters.

Connection & DNS Errors

These are more network- or domain-related.

• 421 4.4.2 Connection dropped
  Receiving server closed the connection unexpectedly.
• 450 4.4.1 Host not found
  DNS lookup failed for the recipient’s domain.
• 550 5.4.4 Routing loop detected
  Message got stuck in a routing loop between servers.

Tip:
Permanent failures (5.x.x) mean the sender needs to fix something (address, authentication, policy). Temporary failures (4.x.x) usually resolve on their own, unless persistent.

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