I bumped into a interesting problem while testing latest /e/ builds. I use K-9 rather than /e/'s fork and, to save time, I have exported email settings which I import on new installations. Recent versions of K-9 allow the app to continue after importing setting without entering account passwords. With 5.600 and earlier versions I had to enter passwords immediately after importing the settings. What seems to happen now is that K-9 repeatedly attempts to login to the email server without a valid password, and eventually triggers fail2ban (or whatever else the provider uses to protect the server).
I only discovered this when my email provider started rejecting connections from Thunderbird and the webmail interface using a browser. These connections were using the same internet connection - my home broadband and wifi - as the phones. Short term solution was to connect from a different IP address (using the phone’s mobile internet, or resetting the router which picked up a new IP address).
I don’t think this will be a problem for /e/'s Mail, which is currently based on v5.600 unless / until it is changed to use the latest version of K-9
I have raised an issue with K-9 (App attempts to connect to accounts before password has been entered · Issue #5576 · k9mail/k-9 · GitHub) but there is no guarantee it will be fixed any time soon