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553 SMTP Relaying Denied error received from mkryptor SMTP Listener

Last Updated: Jun 18, 2013 05:14PM BST


When sending a message to the mkryptor SMTP listener, the message is rejected with the error message "553 SMTP Relaying Denied."

The sender may also receive a Non Delivery Report from mkryptor stating "You are not authorised to use this service when sending from the address xxxxx@yyyyy.com"


The 553 SMTP Relaying Denied message is given when the message FROM: address does not match a domain/email address that is authorised / licensed to use the mkryptor service

By default, mkryptor will not act as an open relay. If you wish to enable relaying, you must set the 'Allow Relaying' option.


If you are NOT trying to relay messages

Note: If you are using Exchange server and some mailboxes are configured to forward messages to external addresses, then this is treated as a relay. In which case see 'If you ARE trying to relay messages' (below)
First check that the account you are trying to send the message from is authorised/licensed in mkryptor:
  • Open mkryptor configuration manager
  • Select the Mail Out tab
  • Check that the Sender Domain / address is specified correctly on the 'Mail Out' tab.
check sender domain on mailout tab


If you ARE trying to relay messages

​If you need to relay messages for other domains / users, then you must check the 'Allow Relaying' option on the Mail In tab:

NOTE: When using the 'Allow Relay' option it is advised to ensure that your mkryptor server does not become an Open Relay by doing at least 1 of the following:
  • Ensure a firewall is blocking connections to mkryptor from the internet
  • Configure authentication on the SMTP listener (See article: Configure Inbound SMTP Authentication).
  • Add an IP Filter in the IP Filter box so that mkryptor will only accept connections from designated IP address(es) (i.e., your mail server(s)

When relaying, messages that do not match a Sender Domain / licensed domain will be passed-through mkryptor unchanged and mkryptor will ignore any tags in these messages. 
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