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Thunderbird email rejected by Barracuda

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  • Last reply by jlearwig

jlearwig
jlearwig
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Thunderbird being used as IMAP client for Gmail - with no issues, until recently when an existing email recipient, who sits behind the Barracuda Networks system, fails to receive mail from Thunderbird's recent versions because it is rejected and blocked by Barracuda. I have tried using plain text formats and checked that SMTP server accounts are correct all to no avail, a 550 blocked is the result. The Thunderbird ver is 143 64 bit - However mail from an earlier 32 bit version 115.5 was successfully delivered, later 32 bit ver 140 failed to deliver through the Barracuda system.

Email from Google's own Web client gets delivered and mail from the Android mobile phone app likewise arrives. A simpler IMAP client (MailSpring) manages to get mail thru Barracuda so what has Thunderbird done to appear a threat to Barracuda ? BTW Mailspring is sort of 'Ok' - but it just isn't Thunderbird - it was installed only as a test vehicle !

Thunderbird being used as IMAP client for Gmail - with no issues, until recently when an existing email recipient, who sits behind the Barracuda Networks system, fails to receive mail from Thunderbird's recent versions because it is rejected and blocked by Barracuda. I have tried using plain text formats and checked that SMTP server accounts are correct all to no avail, a 550 blocked is the result. The Thunderbird ver is 143 64 bit - However mail from an earlier 32 bit version 115.5 was successfully delivered, later 32 bit ver 140 failed to deliver through the Barracuda system. Email from Google's own Web client gets delivered and mail from the Android mobile phone app likewise arrives. A simpler IMAP client (MailSpring) manages to get mail thru Barracuda so what has Thunderbird done to appear a threat to Barracuda ? BTW Mailspring is sort of 'Ok' - but it just isn't Thunderbird - it was installed only as a test vehicle !

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david
david
  • Top 10 Contributor
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Please post the complete error message. Often, a 550 error message includes additional numbers that clarify the error. A common one is relaying.

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jlearwig
jlearwig Question owner
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HI David Thanks for your reply & prompt reply However, There were no other error codes I copy here the text one of the several returns which were all very similar only differences were time stamps

" ...XXXXX = sending email address yyyyy = recipient email addresss wwwww = recipient domain

Reporting-MTA: dns; googlemail.com Received-From-MTA: dns; xxxxxxxxxxxxxxxx Arrival-Date: Wed, 08 Oct 2025 09:40:07 -0700 (PDT) X-Original-Message-ID: <259ce764-0a0a-4aad-ad9b-12d8223ad615@googlemail.com>

Final-Recipient: rfc822; yyyyyyyyyyyyyyy Action: failed Status: 5.7.0 Remote-MTA: dns; d55365a.ess.barracudanetworks.com. (209.222.82.252, the 

server for the domain wwwwwwwwwwwww.)

Diagnostic-Code: smtp; 550 permanent failure for one or more recipients (yyyyyyyyyy:blocked) Last-Attempt-Date: Wed, 08 Oct 2025 09:40:09 -0700 (PDT) "

I have redacted email addresses as the recipient address is his personal info I have also added the screen shot of the graphic received.

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