I use a number of different email clients with my IMAP server. To make sure my Mac's Mail.app uses the right mailboxes for Trash, Sent, etc, I did the following:
- Select the folder on the server you want to use for, say, Trash
Go to Mailbox > Use this mailbox for > Trash
- Do the same for Sent and Junk
Gmail settings
- Store draft messages on the server - checked
- Store notes in the inbox - checked
- Store sent messages on the server - unchecked
- Delete sent messages when - never
- Store junk messages on the server - checked
- Delete junk messages when - never
- Move deleted messages to the trash mailbox - checked
- Store deleted messages on the server - checked
- Permanently erase deleted messages when - never
See: