Apple Mail very slow to load up and close down
Problem started about 4 weeks ago. I'm using an iCloud account, that's not massive at 1.5 GB. Same issue on Big Sur and still happening after upgrade to Monterey. Tried disabling and re-enabling mail and also multiple mailbox rebuilds. Connection doctor comes up saying everything is fine. My email works perfectly fast using Spark email client. By broadband is circa 350 Mbps.
My conclusion is it's something related to Apple Mail.
Any ideas how to fix?
James
MacBook Air (2020 or later)