Discuss whether we want to enable automatic email checking

Originally created by @segfault on #17282 (Redmine)

Context

We started this discussion in #17222 (comment 4426) and following. We did not reach a conclusion in time for 4.1, so we kept the behavior of previous Tails version, which is to disable the automatic email checking.

Before 4.1 the user could opt-in for automatic email checking (with or without being conscious of the privacy implications), but since 4.1 it’s impossible.

Scope

• fetch email automatically when Thunderbird starts
• fetch email regularly in the background

In favor of enabling automatic email checking

• better UX for a subset of our userbase

In favor of disabling automatic email checking

• email server admins can correlate multiple contextual identities hosted on the same email server
  • rebuttal: officially we don’t “support” using several contextual identities in a single Tails session (weak as users do it anyway in practice, and as long as we don’t forbid this nor warn them while setting up a 2+’th email account, that’s expected)
  • rebuttal: at least in some cases, the “Get Messages” button leaks this info already (it’ll fetch email for every account, unless a specific one is selected already in the sidebar; if “Local Folders” is selected, that button fetches email for every account)

Related issues

• Related to #17222 (closed)