554 Denied

Get reciever to whitelist the sending domain

550 not permitted to relay through this server without authentication.

This appears for POP emails. Enable "Send Authentication" in the Outlook mail settings for the pop account.

5.0.0 smtp; 550 5.1.1 User unknown

This may be resolved by accessing the email/distribution list on the exchange console and unchecking "Require that all senders are authenticated"
  1. Right click the email/distribution list and select properties
  2. Switch to Mail Flow Settings and get into the properties of Message Delivery Restrictions
  3. Un check "Require that all senders are authenticated"


Your message wasn't delivered because of security policies. Microsoft Exchange will not try to redeliver this message for you. Please provide the following diagnostic text to your system administrator.

#5.7.1 smtp;550 5.7.1 RESOLVER.RST.NotAuthorized; not authorized> #SMTP#

  • You might have to contact this recipient. Based on the bounceback message, their spam server blocked your email. Please request to have your email/domain added to their whitelist/allowlist.

#< #5.0.0 X-Spam-&-Virus-Firewall; host <MAIL SERVER> <IP> said: 550 5.7.1 Message rejected as spam by Content Filtering.
  • If the error is pointing to your MAIL SERVER access the Exchange Console and do the following
  1. Open Organization Configuration
  2. Click Hub Transport
  3. Click on the Anti-spam tab
  4. Right Click Content Filtering and select properties
  5. Switch to the Exceptions tab
  6. Add the email address that is getting blocked by content filtering and click Add

There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.

<domain.name> 5.5.0 smtp;553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)

This is an issue on their end. They have a list of approved domains that can be received.
You will need to advise them to add the <domain.name> domain(s) to that list.

No Recipient Succeeded

450 4.5.0
Message appears in queue on Exchange 2007 server

1. Open the Exchange Management Cosole and access Hub Transport from within Organization Configuration

2. Switch to send connectors and edit the connector being used.
3. Switch to the Address Space tab and click Add.
4. Type *.<domain.name> and the messages should leave the queue

5. Restart the Microsoft Exchange Transport service

#5.5.0 smtp;550 Junk Mail Rejected - <domain> [IP]

The <domain> with mail server [IP] has been blacklisted and a request for removal needs to happen

550 4.4.7 QUEUE.Expired; message expired

Check for blacklist at receiving/sending domain

#5.0.1 server error - malformed address

Delete cache'd contacts in address book cache and try sending again

#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

Clear the users NK2 cache:
  1. Open Outlook
  2. Create a new blank email message
  3. In the “To” field where you normally type email addresses begin typing an email address
  4. When you see the email address autofill press the down arrow to select it. Once it is highlighted press delete.
  5. Once again, in the “To” field type the same email address and try to send a test email.

This will clear out the cached copy of the email address stored in the NK2 file in the Outlook address book and replace it with a new one.

If this doesn't work you have to remove the entry from the GAL (Global Address List)
external image ZA010274320.jpg

  1. On the Standard toolbar, click Address Book
TIP You can also open the Address Book by clicking Address Book on the Tools menu.
  1. Click Tools, and then click Options.
NOTE If you open the Address Book from an open message, the Tools menu is not available. The Address Book must be opened by either method described in Step 1.
  1. In the Show this address list first box, click the name of the address book that you want.
  2. Click OK, and then close the Address Book.

Host < host name>: 550 Relay not permitted

When you switch between 2 email hosting provider sometimes your email attempts to get sent through the old hosting company instead of the new one. When this happens you get the "550 Relay not permitted bounce back message".

2 things to do to fix:
Remove the cache contacts for the email that is causing this bounce back
Contact the hosting company in <host name> and have them remove the old records that are causing the bounce back