I'd rather have all my data myself so I could pick great features from anyone who makes them. Nylas sounds like a part of the puzzle to make that happen. I wish you guys the best of luck.
In terms of privacy, the experience is good. I must warn, though, it's quite unpleasant in terms of dancing pigs and bunnies[1]. You won't get anything fancy. The age of protocol development had passed long ago and mail protocols (IMAP) aren't evolving anymore. Almost all the modern stuff is proprietary to services and their APIs and clients.
This limitation doesn't apply to mail filtering and automated parsing, though. Mail filters and processing for self-hosted email is way more powerful one can normally get with third-party services.
It happens that I'm right in the middle of configuring my own server. I've got only postfix and dovecot for now, nothing fancy yet.
If this is not powerful enough, you can make sieve plugin invoke external program and pass it MIME-encoded email message for further processing. This way your server can, for example, add events to your calendar software or do the accounting based on receipt emails (and I forward my SMS to my IMAP server too)
Before Sieve I've used tools like procmail (http://tldp.org/LDP/LG/issue14/procmail.html), although I'm currently only using Dovecot/Sieve setup for my own mail. Some servers I've configured, for example a DIY SMS gateway at the company I've worked for, use just postfix+procmail (+ custom bash and Python scripts).
As for the spam filtering, I've had a good experience with rspamd (https://rspamd.com/), which is light on resources, integrates with Postfix quite nicely, usable out-of-box and is scriptable with Lua.
Hope those few pointers would help.
Thanks a lot for recommending Sieve, I really mean this. There isn't even a single mention of it on the myriad of the half-baked 'how to setup isp-mail for personal use' blogspam I keep stumbling into when googling issues.
It looks like a great tool. Now I can probably have 'n' junk mailboxes with varying personal filters (always wanted this).
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