There are a bunch of other 'efficient' mail apps, but if you just need basic features and don't go for some exotic or trendy workflow, Mail works fine.
I don't upgrade to the latest OS for at least a few weeks, though, because if something like this is systemic, it will be fixed in the .1 or .2 release.
Also, always keep at least one local backup (I have Time Machine for that), and at least one remote backup.
It's really hard to find apps like that, and I often feel like it's getting harder as time goes on.
If I was someone continually running into issues as some seem to continually have happen I might not feel that way, but I've been on the Catalina and iOS 13 betas and thankfully even with the betas didn't have issues.
EDIT: I did have earlier versions of the iOS betas duplicate draft messages. Which lead to confusion and double sending since at first glance it looked like like I hadn't sent a message in drafts; once I figured out what was going on I would just check my sent to make sure I sent it before deleting the dupe in drafts. At least it wasn't a data loss bug.
When I need a more featured alternative to something I'll use one (Things instead of Reminders, OneNote instead of Notes, VLC instead of QuickTime, etc) but email hasn't been one of those things.
Is there a reason that I should be looking at Mail alternatives? What important features is it lacking?
2. It allows me to have 7 inboxes routed to one view
3. It's pretty fast.
4. While "boring", It usually" just works.
I also just use macOS/iOS Mail because FastMail can push notify to the clients, and FastMail's iOS app isn't ideal.
I’m not opposed to switching but everything looks pretty lousy, in terms of workflow and integration, and if I have to live with “pretty lousy”, then “zero cost” and “mainstream first-party offering” seem to be the way to go.
I have Thunderbird installed for accessing a large e-mail archive on my NAS (simply because it has more control over local copies of messages) and find it horribly clunky and un-Mac-like even today.
And none of the trendy, flashy "new inbox philosophy" apps that have come and gone over the years were any sort of an improvement.
Even though I work at Microsoft today and acknowledge that the Entourage dumpster fire was finally fixed in the modern versions of Outlook for the Mac, I still prefer Mail.app because of its simplicity and straightforwardness, and refuse to use anything else for my personal e-mail.
Which is why I won't be upgrading to Catalina until this data loss bug is fixed...
And there’s nothing particularly wrong or bad about it (until now, maybe).