The managers of a group may choose to create one or more subgroups in that group, as distinct from creating additional separate groups. With a few exceptions a subgroup of a group has the same features and controls as any other group, including the parent group.
It is those exceptions which matter when considering whether to make a subgroup to an existing group, or a separate group.
Related Identity
One reason to use subgroups is that their email and web addresses have a common identity with those of the parent group.
Subgroups may be listed on the parent group's home page; each subgroup has a Privacy setting to control this. A link back to the parent group is automatically placed on the subgroups' home pages.
Subdomain addressing
When a group named "example" has no subgroups, its web address and email posting address are written as:https://groups.io/g/example
example@groups.io
When one or more subgroups are created in a group the address format is changed: the primary group name becomes a "subdomain"[1] in the web and email addressing, and the subgroup names take the place of the primary group name:
https://example.groups.io/g/main
https://example.groups.io/g/Sub-A
https://example.groups.io/g/Sub-B
And the corresponding email posting addresses:
main@example.groups.io
Sub-A@example.groups.io
Sub-B@example.groups.io
The default name "main" for the primary group can be changed by the group managers, if they feel there would be a better name to identify the primary group. This field is referred to as an alias for the primary group name.
Legacy addressing
Prior to April 2016, subgroup names were suffixed to the primary group name as follows:
https://groups.io/g/example
https://groups.io/g/example+Sub-A
https://groups.io/g/example+Sub-B
And the corresponding email posting addresses:
example@groups.io
example+Sub-A@groups.io
example+Sub-B@groups.io
For backward compatibility the legacy addresses are accepted when browsing the web or in emails addressed to Groups.io. They are no longer included in outbound email messages nor presented on the web site.
The relevant announcement along with examples can be found in this Update announcement group post.
Related members and management
One reason to use subgroups is that it can ease the management of group memberships.
The Subgroups page shows all parent group members, with checkboxes to control their subgroup memberships (add or remove).
Subgroup members must be members of the parent group
People who attempt to join a subgroup, and are not yet members of the parent group, join the parent group instead. Then they may join the subgroup. If either or both the parent group or the subgroup have restricted membership then moderator approval will be required at that step.
There is no Invite feature in a subgroup, people must be invited to the parent group.
If a subscriber leaves or is
removed from the parent group, that subscriber is automatically removed
from all of the subgroups.
Direct Add
There is a
Direct Add feature in subgroups. Unlike Direct Add in the parent group
it is available even in Basic ("free") groups, but it applies only to
members of the parent group.
Open or Restricted subgroup membership
Subgroup membership can be open to parent group members, even when parent group membership is restricted.
Owners and Moderators
The
owners and moderators of the parent group are automatically owners and
moderators of all subgroups. This is an important feature for retaining
control in groups that allow members to create subgroups.
Access Controls
Features in the subgroup can be made visible to parent group members, while still being hidden from the public.
The ability to create subgroups can be given to Members of the parent group. If a member creates a subgroup that member is automatically an owner of the subgroup.
Examples
Some example use cases for subgroups.
Moderators' group
A common desire is to support better communication among the management of a group. In Y!Groups and other email lists this is sometimes achieved by creating a separate group, whose membership is restricted to just the moderators and owners of the primary group.
This is a natural use case for a subgroup.
PTA group
Primary group is all PTA members, subgroups for board, teachers, school admin, and students.
Product support
Main group for general questions, subgroups dealing with specific topics such as beta testing or off-topic chats.
The official Groups.io user documentation is in the Groups.io Help Center.