mbsync slow gmail All Email folder with +100K emails

[Martin C. <mar...@gm...>]

I am using mbsync (isync 1.4.4) on Ubuntu to sync Gmail imap to my local
machine.

The Gmail All Mail folder has +100K emails and takes a very long time to
sync. Looking at the output from mbsync --debug there is not a lot of
network traffic, but it appears that for EVERY email in the All Mail folder
there are entries like this:
 ```
 entry (1,1,16,)
 ...
 uid=5750  flags=S    size=0      tuid=?
 ...
 pair (53571,21018)
 ...
 F: * 21018 FETCH (UID 53571 FLAGS (\Seen))
```

The entire output of the --debug command is approx. 24 mb, which I have
saved as a log file.

So it appears that the slowness is local.Any idea how I can speed things up?