Sent emails aren't appearing in sent folder on MacBook Air
I've got a problem with my sent mail folder. The emails I'm sending simply are not showing up there. Today all I can see in my 'sent' folder is a random selection of sent mails, the most recent from four days ago. I've sent many emails since then - but they are not appearing, nor are they appearing when I search for them. I know at least some are being sent - I'm getting replies - but I can't be 100% sure on the ones on which I don't have replies. Emailing people saying 'did I reply to you?' feels pretty unprofessional. It's the same on my iPhone. I'm using Mail on the MacBook Air (M2 2022) with OS 12.6.7. Help!
[Re-Titled by Moderator]
MacBook Air