**What happened?** The description of the problem concerns the Thunderbird but also the stand alone version and other sieve editors. I would like to edit Sieve via the plugin/program. My mail account works without problems and can also send/receive. Creating a new account is possible without any problems. As soon as I click on "Connect", the loading bar is permanently there and nothing happens. I have activated debugging in the settings, but I don't know where it is saved. if someone tells me, I can submit the required log later. **Settings** Settings from Sieve: Server imap.xxxxxx.eu: 4190 (Secured connection) Username my at fancydomain.eu **Logs** dovecot-mailcow_1 | May 9 02:47:16 04888203e1b5 dovecot: managesieve-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=92.123.123.123, lip=123.123.123.123, TLS handshaking: SSL_accept() failed: error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate: SSL alert number 42 **What i tried?** 1. gnutls-cli --starttls -p 4190 imap.xxxxxx.eu Output: `Processed 129 CA certificate(s). Resolving "imap.xxxxxxxxx.eu:4190"... Connecting to "2a03:4000:34:522:981b:xxxx:xxxx:xxxx:4190"... Simple Client Mode: "IMPLEMENTATION" "Dovecot Pigeonhole" "SIEVE" "fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext vacation-seconds editheader imapflags notify imapsieve vnd.dovecot.imapsieve" "NOTIFY" "mailto" "SASL" "" "STARTTLS" "VERSION" "1.0" OK "Dovecot ready."` 2. telnet xxx.xxx.xxx.xxx 4190 output: Connected to xxx.xxx.xxx.xxx. Escape character is "^]". "IMPLEMENTATION" "Dovecot Pigeonhole" "SIEVE" "fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext vacation-seconds editheader imapflags notify imapsieve vnd.dovecot.imapsieve" "NOTIFY" "mailto" "SASL" "" "STARTTLS" "VERSION" "1.0" OK "Dovecot ready." 3. Added in dovecot.conf in "service managesieve-login" "ssl = no" and after that "ssl = true" but also not working. dovecot config: service managesieve-login { inet_listener sieve { port = 4190 ssl = no } inet_listener sieve_haproxy { port = 14190 haproxy = yes } service_count = 1 process_min_avail = 2 vsz_limit = 1G } **OS/Software Informations** Client Thunderbird: OS: Windows 10 Sieve Version: 0.5.3 Thunderbird Version: 78.11.0 Client Standalone: OS: Windows 10 Sieve Version: 0.5.2 Mailcow: OS: Ubuntu 20.04 Mailcow Versions: acme-mailcow (mailcow/acme:1.78) clamd-mailcow (mailcow/clamd:1.39) dockerapi-mailcow (mailcow/dockerapi:1.38) dovecot-mailcow (mailcow/dovecot:1.145) ejabberd-mailcow (mailcow/ejabberd:1.5) ipv6nat-mailcow (robbertkl/ipv6nat) memcached-mailcow (memcached:alpine) mysql-mailcow (mariadb:10.5) netfilter-mailcow (mailcow/netfilter:1.41) nginx-mailcow (nginx:mainline-alpine) olefy-mailcow (mailcow/olefy:1.7) php-fpm-mailcow (mailcow/phpfpm:1.74) postfix-mailcow (mailcow/postfix:1.61) redis-mailcow (redis:5-alpine) rspamd-mailcow (mailcow/rspamd:1.76) sogo-mailcow (mailcow/sogo:1.98) solr-mailcow (mailcow/solr:1.7) unbound-mailcow (mailcow/unbound:1.13) watchdog-mailcow (mailcow/watchdog:1.91) -- Sent from: http://dovecot.2317879.n4.nabble.com/