# Thunderbird vs. LetsEncrypt woes

**URL:** <https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578>\
**Category:** Rocky Linux Help & Support\
**Tags:** rocky-linux-8\
**Created:** [June 6, 2026, 6:08am UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578 "2026-06-06T06:08:20Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![microlinux](https://sea2.discourse-cdn.com/flex020/user_avatar/forums.rockylinux.org/microlinux/32/1244_2.png) [@microlinux](https://forums.rockylinux.org/u/microlinux)\
**Post date:** [June 6, 2026, 6:08am UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578/1 "2026-06-06T06:08:20Z")

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Hi,

I’m hosting my own mailserver using Postfix, Dovecot and OpenDKIM on Rocky Linux 8, for my own domain as well as a few others. That setup has been working perfectly for a few years now.

A few days ago, Thunderbird started complaining about LetsEncrypt certificates. On the server, the LetsEncrypt certificates are updated once a month via a cronjob, and then Postfix and Dovecot get restarted. This has always worked well.

Now my phone keeps ringing, because all folks who are using Thunderbird as a client for their mail hosted on my server keep getting the same message.

And I can’t figure out what’s going on. Is this a known problem ? Anybody get the same warnings and error messages ?

Cheers from the sunny South of France,

Niki

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**Author:** ![iwalker](https://sea2.discourse-cdn.com/flex020/user_avatar/forums.rockylinux.org/iwalker/32/2599_2.png) [@iwalker](https://forums.rockylinux.org/u/iwalker)\
**Post date:** [June 6, 2026, 11:20am UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578/2 "2026-06-06T11:20:41Z")

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> [@microlinux](#):
>
> And I can’t figure out what’s going on. Is this a known problem ? Anybody get the same warnings and error messages ?

What are the warnings and errors you are getting? What’s in the log files when someone connects via Thunderbird be it IMAP/POP3 or SMTP? And what’s the error from the Thunderbird client itself?

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**Author:** ![sdw](https://sea2.discourse-cdn.com/flex020/user_avatar/forums.rockylinux.org/sdw/32/6158_2.png) [@sdw](https://forums.rockylinux.org/u/sdw)\
**Post date:** [June 6, 2026, 4:35pm UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578/3 "2026-06-06T16:35:21Z")

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I am having a similar problem. Seems to be a Thunderbird problem, perhaps because of the removal by LetsEncrypt of the client auth flag.

Send Message Error  
Sending of the message failed.  
Peer’s Certificate issuer is not recognized.  
The configuration related to lig dot net must be corrected.

Looking at the certificate in Thunderbird: Everything seems fine. Can’t copy from that view, but valid dates, DNS name, etc. all look normal.

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**Author:** ![microlinux](https://sea2.discourse-cdn.com/flex020/user_avatar/forums.rockylinux.org/microlinux/32/1244_2.png) [@microlinux](https://forums.rockylinux.org/u/microlinux)\
**Post date:** [June 8, 2026, 12:07pm UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578/4 "2026-06-08T12:07:59Z")

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Right, here goes. Here’s what happens when I open Thunderbird with a series of accounts. These are the logs on the server:

```auto
Jun 8 14:04:29 sd-110196 dovecot[1786]: imap-login: Disconnected: Connection closed: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48 (no auth attempts in 1 secs): user=<>, rip=86.193.248.219, lip=163.172.82.215, TLS handshaking: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48, session=<qtoB0LxTEKBWwfjb>
Jun 8 14:04:29 sd-110196 dovecot[1786]: imap-login: Disconnected: Connection closed: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48 (no auth attempts in 1 secs): user=<>, rip=86.193.248.219, lip=163.172.82.215, TLS handshaking: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48, session=<iwkC0LxTFKBWwfjb>
Jun 8 14:04:29 sd-110196 dovecot[1786]: imap-login: Disconnected: Connection closed: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48 (no auth attempts in 1 secs): user=<>, rip=86.193.248.219, lip=163.172.82.215, TLS handshaking: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48, session=<iikC0LxTHKBWwfjb>

```

I’m clueless.

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<div class="post-metadata">

**Author:** ![FrankCox](https://sea2.discourse-cdn.com/flex020/user_avatar/forums.rockylinux.org/frankcox/32/1572_2.png) [@FrankCox](https://forums.rockylinux.org/u/FrankCox)\
**Post date:** [June 8, 2026, 4:02pm UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578/5 "2026-06-08T16:02:37Z")

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> [@microlinux](#):
>
> `SSL alert number 48`

Unknown certificate authority error

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<div class="post-metadata">

**Author:** ![microlinux](https://sea2.discourse-cdn.com/flex020/user_avatar/forums.rockylinux.org/microlinux/32/1244_2.png) [@microlinux](https://forums.rockylinux.org/u/microlinux)\
**Post date:** [June 8, 2026, 4:58pm UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578/6 "2026-06-08T16:58:08Z")

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OK, I found the problem. Looks like LetsEncrypt has been handling certificates differently indeed in the very recent pas.

Here’s the relevant fragment of my `/etc/postfix/main.cf` file :

```auto
smtpd_tls_cert_file = /etc/letsencrypt/live/sd-110196.dedibox.fr/cert.pem
smtpd_tls_key_file = /etc/letsencrypt/live/sd-110196.dedibox.fr/privkey.pem

```

And here’s `/etc/dovecot/conf.d/10-ssl.conf` :

```auto
ssl_cert = </etc/letsencrypt/live/sd-110196.dedibox.fr/cert.pem
ssl_key = </etc/letsencrypt/live/sd-110196.dedibox.fr/privkey.pem

```

On a whim I replaced `cert.pem` by `fullchain.pem` in both files. Here’s Postfix :

```auto
smtpd_tls_cert_file = /etc/letsencrypt/live/sd-110196.dedibox.fr/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/sd-110196.dedibox.fr/privkey.pem

```

And here’s Dovecot :

```auto
ssl_cert = </etc/letsencrypt/live/sd-110196.dedibox.fr/fullchain.pem
ssl_key = </etc/letsencrypt/live/sd-110196.dedibox.fr/privkey.pem

```

I restarted Postfix and Dovecot and everything works perfectly now.

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex020/uploads/rockylinux/original/1X/91b7219eec10e30013422e4df76c1d898711a5d5.svg) [@system](https://forums.rockylinux.org/u/system)\
**Post date:** [August 7, 2026, 4:58pm UTC](https://forums.rockylinux.org/t/thunderbird-vs-letsencrypt-woes/20578/7 "2026-08-07T16:58:50Z")

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