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Error Upgrade to Debian Buster (10)

May 19 07:52:55 web dovecot: imap-login: Error: Failed to initialize SSL server context: Can't load DH parameters: 
error:1408518A:SSL routines:ssl3_ctx_ctrl:dh key too small: user=<>, rip=192.168.1.3, lip=192.168.1.20, 
session=<...>
May 19 07:53:14 web dovecot: imap-login: Error: Failed to initialize SSL server context: Can't load DH parameters: 
error:1408518A:SSL routines:ssl3_ctx_ctrl:dh key too small: user=<>, rip=192.168.1.3, lip=192.168.1.20, 
session=<...>

Solution: https://wiki.dovecot.org/SSL/DovecotConfiguration

1. openssl dhparam 4096 > dh.pem
2. vim /etc/dovecot/conf.d/10-ssl.conf

   #ssl_dh_parameters_length = 1024
   #ssl_dh_parameters_length = 2048
   ssl_dh=</etc/dovecot/dh.pem

3. service dovecot restart