multiserver ispconfig system. 1 webserver also runs the ispconfig interface, another 2 webservers. dedicated mailserver. ispconfig is 3.1.13 roundcube (1.3.6) is installed on each webserver and on the mailserver. all connect to the same roundcube db hosted on the mailserver. default php is 7.2 on ubuntu 18.04, php5.6 and 7.3 installed as additional php's. (all installed using ondrej repo) all roundcube configs are identical. we have a geotrust wildcard certificate for our own domain, the same certificate is used on all servers, located in /usr/local/ispconfig/interface/ssl all ftp/postfix/dovecot certificates link back to these certificate files. openssl_cafile is set to /etc/ssl/certs/ca-certificates.crt in all php.ini files the ca-certificates.crt file is identical on all servers webmail access was working fine on all servers. yesterday I installed php7.4 as an additional php on all 3 webservers. process was identical on each server. webmail is now working fine on the server that runs the ispconfig interface, and on one of the other webservers, on the 3rd webserver it isn't working. I can get to the login screen fine, but when logging in all I get is 'failed to connect to imap server', a customer claims they are getting 'failed to connect to storage server', but I can't replicate that one. I've double-checked, and triple checked everything, and I can't find anything different in any configs on this server. this is the error logged by roundcube: Code: [03-Dec-2019 09:22:58 UTC] PHP Warning: stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages: error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed in /usr/share/roundcube/program/lib/Roundcube/rcube_imap_generic.php on line 1027 [03-Dec-2019 09:22:58 +0000]: <umr9uq87> IMAP Error: Login failed for [email protected] from 18.104.22.168. Unable to negotiate TLS in /usr/share/roundcube/program/lib/Roundcube/rcube_imap.php on line 196 (POST /webmail/?_task=login&_action=login) I've removed tls:// from the default_host setting in roundcubes config.inc.php and the login works, but sending email fails. I don't want to remove tls from the smtp server, or start submitting to port 25. i'm at a complete loss of what else to look at now, I have no idea why it's only affecting this one server, and i'm unable to find any differences. anyone have any ideas? suggestions..