Can I make an external Network the default Network which users join when the join Yammer. By default it's the Home Network (home domain) which they join when they register in Yammer.

Hi Freedomic,

Seems you've posted the same question in Office 365 Communit Yammer forum. Our Yammer support engineer Jonathan Lee has provided a reply to your question there, could you please take a look and see if it's helpful for you?

Thread link: http://community.office365.com/en-us/f/176/t/294326.aspx

If you have any further questions about this, I would suggest you stick with that thread in Office 365 Community Yammer forum as here in this forum, we only discuss questions and feedback for Microsoft Office client.

The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding.

Regards,

Ethan Hua
TechNet Community Support