I'm providing you a link to some Blat alternatives but there are likely others beyond what you'll find listed in this link.I am not sure whether it will work for office 365 or not.
http://alternativeto.net/software/blat/
This will likely require some tinkering on your behalf but the setup should be similar to what have documented for Blat.I think what you are requesting would be a valid enhancement request to have NetBackup be able to send your catalog backup DR file without the use of a 3rd party product. Windows OpsCenter can email reports without a 3rd party utility so suggesting this ability is something that could be reviewed by product management for future NetBackup releases.
https://www.veritas.com/support/en_US/article.000116044
You can even speak with Microsoft support and ask them to provide you any of their homegrown utlity which can send email using SMTP settings from any server to office 365.Netbackup just uses the ability of server to send emails to mail server.
-Sajal
