I used #Thunderbird for all of my work mail because I hate the Gmail interface and I've long suspected that Google deliberately throttle IMAP to push you towards the web. Well, for the last week I've been trying the mail client built-in to #Vivaldi - and I owe Google an apology. Vivaldi's client is fast and responsive where Thunderbird often grinds to a halt. So my assumption is that Thunderbird handles locally-cached mail poorly. Regular "Compact" operations don't help. This makes me sad.