Problem Definition

Currently TLS1.1 is used when email notifications are sent from Bitbucket to Office365, as Office365 incorrectly handles protocol negotiation when SSLv2Hello is a client-supported protocol.
If using Java 11, this causes an exception due to the protocol being downgraded, and emails are not able to be sent at all.
Office 365 will deprecate definitively TLS 1.0 and TLS 1.1 soon.

Suggested Solution

Remove SSLv2Hello from the supported mail protocols Bitbucket Mail Server SMTP Protocol.

Workaround:

1. Ensure that SSLv2Hello is not part of the supported mail protocols by adding the following setting to bitbucket.properties:

   mail.crypto.protocols=TLSv1.2
   

2. Restart Bitbucket