# Help - Solution de secours : panne sur la ligne principale - Serveur secondaire

**URL:** https://forum.yunohost.org/t/help-solution-de-secours-panne-sur-la-ligne-principale-serveur-secondaire/27712
**Category:** Advanced use case
**Tags:** french
**Created:** [December 21, 2023, 7:35pm UTC](https://forum.yunohost.org/t/help-solution-de-secours-panne-sur-la-ligne-principale-serveur-secondaire/27712 "2023-12-21T19:35:50Z")
**Posts on this page:** 1
**Showing post:** 16

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### Author: ![wbk](https://forum.yunohost.org/letter_avatar_proxy/v4/letter/w/e0b2c6/32.png) [@wbk](https://forum.yunohost.org/u/wbk)
#### Post date: [December 23, 2023, 8:41am UTC](https://forum.yunohost.org/t/help-solution-de-secours-panne-sur-la-ligne-principale-serveur-secondaire/27712/16 "2023-12-23T08:41:37Z")

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There was a post a while back from someone not receiving mail, related to a Spamhaus something.

I can’t find the specific thread 1-2-3, but searching for Spamhaus on the forum returns [this thread by Maniack\_Crudelis.](https://forum.yunohost.org/t/trouble-with-spamhaus-marking-any-mail-as-spam/23814)

How Spamhaus determines which DNS resolver is being used, and at which level: no idea (but I do after edit2)

- edit - I found [the other thread](https://forum.yunohost.org/t/recption-email-impossible/27678/11); Aleks suggests it has to do with ports 53/5353 being open on our own server (which would allow DNS amplification attacks, I think, but I wonder why Spamhaus would monitor that). There does not seem to be a resolution in that specific thread.
- edit2 - You know how to use search engines, but that way I found a [blogpost delving into the problem](http://web.archive.org/web/20231205161420/https://www.claudiokuenzler.com/blog/1231/postfix-reject-mails-blocked-using-zen-spamhaus-dnsbl-open-resolver), with a link to a [technical explanation](http://web.archive.org/web/20230530113134/https://www.geekersdigest.com/what-is-dnsbl-how-do-they-work-fight-against-spam-mails/) of DNSBL, which is where the open resolver comes in.

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