No offense but unless it’s a 1st party client email clients are something that is very hard to trust. Who controls your client has access to your inbox with most services even the few that have separate IMAP/POP3 passwords like Hushmail can be compromised through it. If your client also integrates with encryption or worse takes charge of it my encryption key is also now at risk. Lastly since email today is pure HTML…
Few webmail "clients" are open source and many native clients like e.g. Outlook are also not open source, yet these are very popular. Unless you use a highly trustworthy email provider, considerations about client programs are kind of moot anyway. I'd personally be more picky about my mail provider and not use any offerings by Google or Microsoft, for instance, because they are stock market companies with interests t…
And yes choose your email provider based on your threat model but there is nothing wrong with Google or even MSFT for most people security wise privacy is a different concern but these are different threat models.
An email client won’t prevent my email provider from snooping on me (E2E maybe), and no email provider could prevent my client from snooping on me either.