Common Errors



Error code: 550 sorry, you can't send as this user


Symptom: The messages that you send out come back as a bounce message with the following error:

550 sorry, you can't send as this user

Cause: You are not allowed to send emails on behalf of this user. We have enabled a strict check to see if the sender matches the authenticated user, or is related to it somehow.

Solution: Authenticate as the same user you wish to send or log in to your Admin Panel to define other email addresses that can send as this user (Admin Panel → Users → click on Permissions for the desired user → Send email as).


Error code: 550 sorry, you are blacklisted on this server 


Symptom: The sender receives a bounce message with the following error:

550 sorry, you are blacklisted on this server 

Cause: You have blacklisted this sender on our servers.

Solution: Remove the blacklist from your Admin Panel (Admin Panel → Filtering → Blacklist → check Include Users Blacklist → search for the sender's email or domain → remove the entries). Alternatively, you can access your email's User Panel and go to Filtering →  Blacklist → do a Control F and search for the sender's email address, then click on the minus sign next to it, to remove it.



Error code: That sender cannot send mail here 


Symptom: The message is not delivered and in the Incoming Logs the delivery status is Rejected and you see this message:

That sender cannot send mail here

Cause: The sender's domain is blacklisted. Usually, it's a TLD that has a very bad reputation.

Solution: Open a support ticket requesting the whitelisting of the domain.



Error code: You have exceeded your messaging limits


Symptom: When sending out a message, you receive the following error:

451 You have exceeded your messaging limits

462 Daily send limit reached. Please try again tomorrow

Cause: You have sent more than 300 e-mails during the day thus reaching your daily send limit.

Solution: If you did not send that many e-mails, immediately run a full virus scan of your computer, change your email address password or contact your administrator.

In the user control panel, option Track Deliveries, you are able to see how many messages the account has sent out in the last 24h.


Error code: 553 sorry, that domain isn't in my list of allowed rcpthosts


Symptom: The messages that you send out come back as a bounce message with the following error:

553 sorry, that domain isn't in my list of allowed rcpthosts

Cause: SMTP Authentication is not enabled in your e-mail client

Solution: Enable SMTP Authentication in your e-mail client



Error code: 4.4.2

Symptom: The email client is getting the following error:

The server response was: timeout (#4.4.2)

Cause: Your email client hasn't sent a command in 20 seconds

Solution: Verify your email client and internet connection




Symptom: When sending messages out, the server repeatedly asks for your username & password, despite having entered the right ones

Cause: If you are sending out using the regular port 25, it is possible that your local Internet Provider is intercepting SMTP communications on port 25 and forcing you to use their own SMTP servers. Your SMTP credentials would thus fail against their servers

Solution: Change your outgoing SMTP server port to another value. You can use ports 26 or 587 for regular/TLS server or port 465 for SSL service.




Symptom: When someone sends you an email, they get the error below:

 552 cuda_nsu sorry, you are blacklisted on this server 

Cause: You changed default domain or user filtering settings inside the Filtering option. Instead of using the default Accept e-mails from Everyone, such option was changed to Accept e-mails from whitelist and address book only, which means account will receive e-mails only from addresses in the whitelist or contacts and all other e-mails will be rejected.

Solution: Change the mentioned option to Accept e-mails from Everyone. Verify both on admin (domain level) and user control panels, by clicking on Filtering, in the top menu.

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