a) filter conversations by read/unread/has attachments/sender/recipient/date etc.
b) Snooze email much like Reminders
c) add notes to email messages or conversation
a) is already supported. You can filter conversations by all of the criteria you mentioned. In the search bar enter a ? and it will give you a list of keywords to use for searches. It however, does not support “not”.
You can save searches by creating search folders, which dynamically update as data changes.
A workaround for b) is to “flag” an email. This will cause it to display in the “Agenda” tab for future follow-up.