I am missing emails from a a 2-week period this month. I know this because I can see them in my online Google Workspace account. There are CNM files during that same period. Is there a connection? And can CNM file be converted to PMM & PMI files?

Each new message is made up of a single .CNM file. There isn't a way to manually move them into folder files (.PMM/.PMI files).

Try changing the sort order of your New Mail folder then changing it back to your preferred order to see if they might have been out of place from where you expected to see them.

Is it possible that you have an autofilter that moved them to a folder as they arrived?

I removed the message spec. to sort unread first & changing the sort order didn't help. I have no filters.

Why were the CNM files not split? They're all there from the time period during which PMM/PMI files are missing. There's no tool that would do it?

I am confused. I don't know the relevance of your reference to missing PMM/PMI files. Those are folder files; PMM contains the data, PMI contains the index. CNM files are new message files, one for each new message. They get incorporated into folder files when they are moved to a folder.

Perhaps I misunderstood your original question. I read it that you could see CNM files that had timestamps in the range of the missing message time period.

I am the one who misunderstood. I had things reversed. was thinking the CNM files are the messages. I've searched all files on each of the dates I know messages are missing and find none.

Just to make sure we're on the same page, CNM files are new mail files, one for each message in the New Mail folder.

I don't know how you are searching but if with a file explorer you won't see them if they are now in a folder. I suggest using the Google online access to get a unique as possible word from the From: or Subject: header of one the missing messages and then in Pegasus Mail do a headers only search of "all folders in the selected mailbox". You can do the same search in the New Mail folder (it isn't included in an 'all folders' search. If neither search finds the message then either it got tagged as downloaded but didn't or it was inadvertently deleted.