I upgraded from 4.4.1 to 5.2.4 and I have enabled sending email but not reading email with:

DISABLE_NOTIFICATIONS=" -Datlassian.mail.senddisabled=false - Datlassian.mail.fetchdisabled=true -Datlassian.mail.popdisabled=true"

Sending email with no authentication via Exchange works fine. But using authentication produces the message

An error has occurred with sending the test email:
com.atlassian.mail.MailException: com.sun.mail.smtp.SMTPSendFailedException: 550 5.7.1 Client does not have permissions to send as this sender

Googling found http://community.office365.com/en-us/forums/160/p/77364/296367.aspx#296367 which suggests that this is a response from Exchange when the From address doesn't match the userid that authenticated with Exchange.

Sure enough, when I changed the From address in my mail server configuration to match the user id that authenticated with Exchange, it worked.

This regression is likely going to be a problem for people who have been using different From addresses for each JIRA project in their Notification Scheme configuration (https://confluence.atlassian.com/display/JIRA/Configuring+Email+Notifications#ConfiguringEmailNotifications-Configuringaproject'semailaddress)

More information at https://answers.atlassian.com/questions/114796/jira-unable-to-send-mail-after-5-2-upgrade?page=1#123213

Workaround
Please refer to 550 5.7.1 Unable to Relay Mail From Exchange Server for a list of symptoms and the resolution.