Ask HN: How much do you trust web based email clients?

The numerous bugs and shortcomings of Apple's Mail app in macOS have reached a point that they're significantly distracting me and slowing me down on a daily basis (faulty search function, smart folders don't work, app icon shows a badge with a wrong unread count, etc.). Now I'm looking for an alternative email client for macOS with IMAP support. Some of the email clients that looked like a solid alternative to me (Spark, Polymail, Mailspring) use a backend that store the IMAP credentials. To me, this looks like a additional security risk. I run a small software company and if a third party gains access to my emails (and even send emails from my account), they could cause significant damage. How do you assess these risks? Do you trust these email clients? Which clients do you use?