How do I attach a file in Channels?

In Channels for Mac, add files to the message before sending it. A message supports up to 20 attachments, and each file must contain between 1 byte and 10 MiB. Files use the conversation's access rules.

1. Open the intended conversation and check its participants.
2. In the composer, select Add attachment, then Upload a file.
3. Choose the file and wait for its attachment to appear. Repeat for additional files within the limit.
4. Review the attached filenames and any upload errors. Remove an unwanted attachment from the composer before sending.
5. Select Send, then check the delivered message and open or download the attachment to verify the intended file.

An upload error does not prove that every file failed. Check which attachments are already present before selecting files again. A file larger than 10 MiB must be reduced or shared by another suitable method. If you share a link instead, make sure the recipients have access to its destination.

You must have posting access to the conversation, and it must not be archived. Someone who cannot read the conversation cannot download its attachments merely by obtaining an attachment reference.

Do not treat deleting a message as a complete file-erasure operation. It removes the attachments from that message, but the attachment records and bytes have a separate lifecycle. It also cannot remove copies already downloaded by recipients.