I want to search Gmail for conversations that have a certain number of messages in the thread (more than three, etc.).
Are there filters to show conversations by how many messages are in them?
Gmail advanced filters help indicates that there is no way to filter by number of messages in a conversation.
Thought about this for years:
You can't. Not in Gmail. But you can install an email client such as Thunderbird, sort the mails by subject, and then you can see the number of messages in a 'thread.'
This doesn't filter by number of emails, but in some circumstances it may help to be able to filter by size:
Search for emails above 1kb (1000 bytes)
size:1000 Or above 1mb (1000000 bytes)
size:1000000