Apple Mail Since upgrade to dovecot 2.3.x unable to connect

[Johannes Rohr]

|Dear all,|

|a couple of days ago I upgraded our server from Ubuntu 18.04 to 20.04,
thereby upgrading dovecot from 2.2.x to 2.3.x.
|

|Since then, some older versions of apple's mail.app (bundled with el
Capitano, released in 2016) no longer connect. When I turn on SSL
debugging, I see:|

|Debug: SSL error: SSL_accept() failed: error:14209102:SSL
routines:tls_early_post_process_client_hello:unsupported protocol
imap-login: Debug: SSL error: SSL_accept() syscall failed: Invalid argument|

||

|Unfortunately, it doesn't reveal the name of the unsupported protocol.
Also, what about the failed syscall? Does dovecot try and fail to open
some file?|

|Here are the contents of /etc/dovecot/conf.d/10-ssl.conf:|

|    ssl = yes
    ssl_cert = </etc/ssl/letsencrypt/idaweb-mail.rooot.de/fullchain.pem
    ssl_key = </etc/ssl/letsencrypt/idaweb-mail.rooot.de/key.pem
    ssl_ca = </etc/ssl/letsencrypt/idaweb-mail.rooot.de/ca.pem
    ssl_client_ca_dir = /etc/ssl/certs
    ssl_dh = </etc/dovecot/dh.pem
|

|I would greatly appreciate any hints!
|

|Cheers,|

|Johannes
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