So... it's a hit or miss whenever you invite external partners if they're not using their corporate domains. So... working with freelancers anyone? Use external networks instead - no restrictions there. Or we should wait for the Office 365 Groups to allow external users...
Update: It seems you can't invite external users to the external groups, unless they are existing Yammer users (e.g. they have a home Yammer network), which makes the service 50 % useless.
Going back to External networks if you need to collaborate with just anybody out there without knowing or asking them if they already belong to a Yammer network...
Starting today, we got a hold of the Yammer External Groups feature.
Previously, when people had to collaborate with external parties, they had to go through creating an external network and then create groups in there and invite people. That worked, however it was hard to keep track of which networks are you in and it was tough when you just had to post a quick message, you had to switch networks...
I've already tested the feature and it works surprisingly well - the external groups are clearly listed as such below all the internal groups. When you invite someone, they get the email invite, join and only see the external group they're invited to. Nothing else.
This is the experience for the external user when they join. They see your group along with the network name under their All Company group.
With external networks, a Network Admin could configure whether those external groups could be created by all users or by the admins only. So far I don't see the option to control the external groups creation, but the regular users can't create them in our network. I can also see that the option to create an external network is now gone.
So... enjoy the external groups and say goodbye to external networks.