Slack offers two primary methods for collaborating with external partners: guest access for individual contributors and Slack Connect for organization-wide collaboration. Guest access allows you to invite freelancers, clients, or contractors to specific channels with restricted permissions, while Slack Connect enables real-time communication between entire organizations in shared channels. Both features maintain security by limiting access to only what’s necessary for collaboration.

Key findings from the sources:

• Guest accounts come in two types: Single-Channel Guests (free, limited to one channel) and Multi-Channel Guests (paid, access to multiple channels) ^[2]
• Slack Connect supports up to 250 organizations in a single shared channel, with admin controls for permissions and security ^[3]
• Workspace Owners and Admins must manage guest invitations, and guest access is only available on paid Slack plans ^[2][6]
• Best practices include setting expiration dates for guest access and using dedicated request channels to streamline onboarding ^[5]

Setting Up External Collaboration in Slack

Guest Access for Individual Collaborators

Guest accounts in Slack provide limited access to external users, such as freelancers, contractors, or clients, without granting full workspace permissions. This feature is ideal for temporary or project-specific collaboration, ensuring external parties only see relevant conversations and files. Workspace Owners and Admins control guest invitations, and the feature is restricted to paid Slack plans—free plans do not support guest accounts ^[2][8].

Slack offers two types of guest roles, each with distinct access levels and billing implications:

• Single-Channel Guests: Free to add, but restricted to one channel. They cannot create direct messages (DMs) with full members or join other channels unless upgraded ^[2][9].
• Example use case: A one-time client review in a dedicated feedback channel.
• Billing: No additional cost beyond the workspace’s existing plan.
• Multi-Channel Guests: Billed as regular members, with access to multiple channels as designated by admins ^[2][9].
• Example use case: A long-term contractor working across multiple project channels.
• Billing: Counts toward the workspace’s total member limit.

To invite a guest, follow these steps:

1. Navigate to the channel where the guest should collaborate.
2. Click the channel name > Settings > Add people.
3. Enter the guest’s email address and select their guest type (Single- or Multi-Channel).
4. Assign the guest to the specific channel(s) they need to access ^[2][8].
5. Set an expiration date (optional but recommended for security) ^[5].

Guests have restricted permissions by default:

• They cannot create public channels, manage workspace settings, or invite other guests ^[2].
• They can post messages, upload files, and react to content in their assigned channels ^[8].
• Admins can further customize permissions, such as disabling file downloads or limiting @mentions ^[9].

Best practices for managing guest access include:

• Creating a dedicated request channel (e.g., help-guests) to centralize and triage guest onboarding requests using emoji reactions or templates ^[5].
• Setting automatic deactivation for guest accounts after project completion to reduce security risks ^[2].
• Regularly auditing guest lists to remove inactive or unnecessary accounts ^[8].

Slack Connect for Organization-Wide Collaboration

Slack Connect extends collaboration beyond individual guests, enabling real-time communication between entire organizations in shared channels or direct messages (DMs). Unlike guest access, Slack Connect allows external organizations to retain their own workspace while participating in a joint channel, with up to 250 organizations supported per channel ^[3][6]. This feature is available on paid plans only, though Slack Connect DMs are accessible on all plans, including free tiers ^[3].

Shared channels via Slack Connect function as a bridged workspace, where:

• The creating organization owns the channel and manages its settings, but all participants can contribute equally ^[3].
• External users retain their own workspace’s security policies, such as data retention and compliance rules ^[7].
• Apps and workflows can be used, though some functionalities (e.g., certain bots) may be restricted based on the external organization’s permissions ^[3].

To set up a Slack Connect channel:

1. Open the channel you want to share (or create a new one).
2. Click the channel name > Settings > Slack Connect > Add people.
3. Enter the email addresses of external users (they must be on a paid Slack plan).
4. Select their permission level: - Post Only: Can send messages but cannot invite others or use workflows ^[7]. - Full Access: Can invite coworkers, use workflows, and retain channel history ^[7].
5. Send the invitation. Admin approval may be required depending on workspace settings ^[6][7].

Key limitations and considerations:

• Private channels (e.g., general) cannot be shared externally without converting them to Slack Connect channels ^[10].
• Pending invitations can be revoked if unaccepted, and admins can adjust permissions post-approval ^[6].
• Profile visibility is controllable; organizations can limit what external users see (e.g., job titles, contact info) ^[3].
• Security features include enterprise-grade encryption, data management tools, and the ability to audit connections via Admin Tools ^[3][7].

For direct messages (DMs), Slack Connect allows one-on-one communication with external users without requiring a shared channel:

• Available on all Slack plans, including free tiers ^[3].
• Initiated by sending an invitation via the Direct Messages section in Slack.
• External users must accept the invitation before communication begins ^[3].

Best practices for Slack Connect include:

• Defining clear guidelines for external collaboration, such as confidentiality agreements and professional conduct rules ^[7].
• Regularly reviewing shared channels to ensure only necessary participants remain ^[5].
• Using emoji reactions or pinned messages to streamline communication in high-traffic shared channels ^[5].