Passing on this tip in case someone else ever runs into this issue. A month ago, Mail started taking 40 seconds or more to open. I keep Mail tidy and lightweight, deleting any emails older than 18 months, removing attachments, not too many rules, etc. so never had this issue before.

Remembered seeing something in the Onyx app, so opened it up, and sure enough, they have a Rebuild Mail index (or a Delete Mail index), and chose the Rebuild and restarted. Mail now opens in under 3 seconds.

Onyx continues to rock. And still free (I'm on M1 Mini on Monterey 12.3.1)

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M1 2020 Mac mini (16G 2T) • Sonoma 14.x • Dual 27" Dell S2722QC monitors • M2 2022 13" MBAir (512G 16G) •

[support.apple.com]

Yeah, rebuild is built-in.

rebuild is built in, but I have found that Onyx seems to do a better job in that Mail isn't dumb the next time I open it after letting Onyx do it.
YMMD.
Onyx once every 3 mos or so id like a good dental check up.

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!#$@@$#!

never do yesterday or today what you can put off til tomorrow or next year.

I've fought this problem in Mail on Big Sur. Frustrating. There's a long thread on MacUsers about it.

[forums.macrumors.com]

Doing as directed in the following post has helped me. But it seems to only last for about a month or so.

- - - - -
Killing (force quitting) the 'fseventsd' service manually via Activity Monitor stopped the long open time for Apple Mail for me. Apple Mail on my M1 MBA had started taking 1-2 minutes to open. It's been driving me crazy for weeks. I've tried all the previous tips, like deleting ~/Library/Mail/ (a.k.a. ~/Library/com.apple.mail/), removing preferences, and disabling extensions, but nothing worked until I saw this post about 'fseventsd' service.

Still on Catalina apple mail, recently paired it down from 230 GB archive to about 70 GB. thousands of attachments received and sent. My sent box was 80 GB all by itself. (still cant figure it out, I've deleted everything from sent and its still 12 GB)

Even on my 2014 iMac, no more than 1 bounce to open. years and years of emails, maybe 100000 emails, at least 50 rules.

its POP, since iMAP cant handle my workflow, so maybe faster cause it doesn't hit a server first?

I still don't like Catalina getting rid of headers "sort, date, size, etc" -- huge kludge, but have learned to live without it.

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Edited 999 time(s). Last edit at 12:08PM by jdc.

I'd done that internal Mail rebuild, but the problem persisted. I'd bet that Onyx uses the same process as the Mail rebuild, but only Onyx worked for me. It's really delightful to have Mail opening again at 2 or 3 seconds.

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M1 2020 Mac mini (16G 2T) • Sonoma 14.x • Dual 27" Dell S2722QC monitors • M2 2022 13" MBAir (512G 16G) •