Mastodon relays are tools that broadcast public posts from one server to many others. When you enable a relay, your posts reach a wider audience beyond your instance. However, relays have built-in limits that affect how far your posts actually travel. This article explains what those limits are and how they shape the reach of your content.
Key Takeaways: Mastodon Relay Discovery Limits
- Relay subscription approval: An instance admin must approve each relay subscription before the relay starts forwarding posts.
- Post visibility filter: Relays forward only public unlisted posts; direct and followers-only posts are never relayed.
- Federation delay: Relays introduce a propagation delay that can range from seconds to several minutes depending on relay load and instance size.
How Mastodon Relays Work and Where Limits Begin
A relay is a separate server that subscribes to public posts from multiple Mastodon instances. When an instance connects to a relay, it sends a copy of every new public post to the relay. The relay then redistributes that post to all other connected instances. This process is called relayed federation.
The main limit on how far a post travels is the relay’s subscription list. A relay only forwards posts to instances that have explicitly subscribed to it. If an instance does not subscribe to the relay, it never receives posts through that relay. This means that even if you post on a large instance, your post will not reach instances that are not connected to the same relay or that use a different relay entirely.
Another limit is the relay’s capacity. Each relay has a maximum number of subscriptions it can handle. When the relay reaches that limit, it stops accepting new subscriptions. The relay operator sets this limit based on server resources such as CPU, memory, and bandwidth. Once the limit is hit, no new instances can join, and your posts stop reaching new audiences through that relay.
Relays also have a geographic or administrative limit. Many relays are run by communities or organizations that restrict subscriptions to instances that follow certain rules. For example, a relay for educational instances may only accept subscriptions from .edu or school-run instances. If your instance does not meet those criteria, the relay will reject the subscription request, and your posts will not travel through it.
Post Visibility Rules
Relays only forward posts with public visibility. Posts set to unlisted, followers-only, or direct are never relayed. This is a hard limit built into Mastodon’s relay code. Even if an instance is subscribed to a relay, a followers-only post from that instance will not be sent to the relay. The post stays within the original instance and its direct followers only.
Instance-Level Relay Limits
Instance admins can also set limits on how many relays their instance connects to. Some admins limit the number of relays to reduce server load. Others disable relay connections entirely for security or moderation reasons. If your instance admin has set a low relay limit, your posts may travel through only one or two relays, reducing their overall reach.
Steps to Check and Manage Relay Reach
To understand how far your posts can travel through relays, you need to check which relays your instance is connected to and what limits apply. These steps are for instance admins or users with admin access.
- Open the relay administration page
Log in to your Mastodon instance as an admin. Go to Preferences > Administration > Relays. This page lists all relays your instance is currently subscribed to. - Review the relay subscription status
Each relay shows its status: enabled, pending, or disabled. An enabled relay is actively forwarding posts. A pending relay means the subscription request has not been approved by the relay operator yet. A disabled relay means the subscription was rejected or removed. - Check the relay’s subscription limit
Click the relay name or URL to visit the relay’s public status page. Many relays display their current subscriber count and maximum limit. If the count is close to the limit, the relay may stop accepting new subscribers soon. - Add a new relay if needed
To expand your reach, click the Add Relay button on the Relays page. Enter the relay’s URL (for example, https://relay.example.com/inbox). Click Submit. The relay operator will review your request and approve or deny it based on their criteria. - Test post propagation
After adding a new relay, post a public toot. Wait a few minutes, then search for that toot on an instance that subscribes to the same relay. If you see the toot, the relay is working and your post traveled through it.
Common Relay Issues That Limit Post Reach
Relay Subscription Pending Indefinitely
If a relay subscription shows as pending for more than 24 hours, the relay operator may not have reviewed the request. Some relays have manual approval processes that can take days. Contact the relay operator directly through their website or email to check the status. If no response, remove the pending relay and try a different one.
Relay Enabled but Posts Still Not Reaching Other Instances
This usually happens when the target instance is not subscribed to the same relay. Even if your instance is connected to a relay, posts only travel to instances that have also subscribed to that relay. Verify that the target instance has an active subscription to the same relay. You can check by asking the admin of the target instance to look at their relay list.
Post Not Visible on a Specific Instance Despite Shared Relay
If both instances use the same relay but a post is still not visible, the issue might be moderation. The target instance may have blocked the source instance or the specific user. Go to Preferences > Moderation > Domain Blocks on the target instance to see if the source domain is blocked. If it is, the post cannot travel to that instance even through a relay.
Relay vs Direct Federation: Post Reach Comparison
| Item | Relay Federation | Direct Federation |
|---|---|---|
| Post visibility | Public only | Public, unlisted, followers-only, direct |
| Propagation speed | Delayed by seconds to minutes | Near real-time |
| Reach control | Admin chooses which relays to subscribe to | User follows accounts individually |
| Server load | Higher load on relay server | Higher load on each instance |
| Moderation | Relay operator can block instances | Each instance admin blocks domains |
Relay federation is best for reaching a broad audience quickly without requiring individual follows. Direct federation gives you more control over who sees your content but requires more manual effort to build an audience.
Understanding these limits helps you choose the right strategy for your posts. If you want maximum reach, connect to multiple relays that accept your instance. If you need privacy, rely on direct federation and avoid relays altogether. Check your instance’s relay list regularly to ensure your subscriptions are active and your posts travel as far as possible.