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Delivery of message aborted after 24 hours

  • 2 replies
  • 1 has this problem
  • Last reply by M

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I use Thunderbird as a client on a MacBook with Catalina. I have been receiving the following error message for emails sent to accounts from various providers like,, and "This is an automatically generated Delivery Status Notification. Delivery to the following recipients was aborted after 24.3 hour(s):" I wrote to the host of the domains of the sending email accounts, and their response is that the error could originate from some settings of the client which may create a security issue with the recipient's domain. I am attaching of these delivery status notification messages with full headers. Do you have any clue on how to fix this? Thank you very much.

Attached screenshots

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Only the domain refusing to accept the mail can tell you why they refuse it. Some make it obvious in stating the address does not exist.

Interesting about the only useful information is probably obscured by the screen shot button.

The error code 5.1.1 generally has a number of common responses. Which applies to you I have no idea.

The most common 550 5.5.1 messages

   550 5.1.1 : The email account that you tried to reach does not exist
   550 5.1.1 : Recipient rejected
   550 5.1.1 : User unknown
   550 5.1.1 : Recipient address rejected: User unknown in virtual alias table

Given the mail is to and is being processes by Aruba, the obvious question is the From: showing an aruba address or something else. Mostly such issues occur when folk send mail from a private domain using mail server that does not belong to the email address.

TheMX record for list permitted senders as So is the sending email address from there?

The check I linked above also identifies a problem with reverse DNS. This is crucial when sending to Microsoft sites that this stuff actually work, not return errors.' That however is an issue for Aruba to resolve.

ERROR: No reverse DNS (PTR) entries. The problem MX records are: -> no reverse (PTR) detected
You should contact your ISP and ask him to add a PTR record for your ips


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Hi Matt,

Thank you very much for your assistance. I have double checked the Delivery Status Notification email and there is no further specification of the 5.1.1 code error hidden in the screenshot: it’s just Action: failed – Status: 5.1.1 I have sent multiple emails from this account to addresses from which I received this error message, but I received the error message only for some of these emails, therefore I don’t have any doubts about the “genuinity” of the recipient email addresses (I know personally the recipients) and I don’t think that any of the most common 550 5.5.1 messages that you listed apply in this specific case. The sending email is from a domain I have with Aruba (an Italian internet provider) and it’s a paid business service and not a free one. This email account is in the form @domainname and has been configured on Thunderbird following Aruba’s instructions (server; outgoing server, therefore I guess the configured mail server belongs to the email address (and I have been experiencing issues with hotmail recipients, not others). I will open a ticket with Aruba for the issue with reverse DNS. In the meantime, thank you very much again for your valuable advice.


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