From: Apple Product Security
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APPLE-SA-2015-04-24-1 OS X Server v4.1

OS X Server v4.1 is now available and addresses the following:

Dovecot
Available for:  OS X Yosemite v10.10 or later
Impact:  An attacker may be able to decrypt data protected by SSL
Description:  There are known attacks on the confidentiality of SSL
3. [...]