What are Plain's attachment size limits when replying to threads?
Plain limits the combined size of all files in a single reply, and the limit depends on the channel type of the thread. It applies to the total of all files in one message, not to each file.
Limits by channel
- Email threads: 6 MB
- Slack threads: 50 MB
- Chat threads: 100 MB
- Microsoft Teams threads: 50 MB
- Discord threads: 50 MB
- Internal notes: 50 MB
- Custom timeline entries: 50 MB
Can the limit be raised?
No. The 6 MB email limit is a hard cap set by Plain's email delivery provider and cannot be increased. There is no workspace setting to change it. The limits on the other channels are set by Plain and are not configurable per workspace.
What to do when files are too large
- Split the files across several replies. This works for Slack and Chat threads when one batch exceeds the limit.
- Compress or resize the files before sending. This is the most reliable option for email threads.
- Share a link instead. If the files are in Dropbox, Google Drive or on a CDN, put a link in the reply body rather than attaching them.
What happens when you exceed the limit
When you select files in the composer, Plain checks their combined size before uploading. If the total is over the channel's limit, the upload is blocked and an error message explains why. Remove files until the total is within the limit, then send.