Just a word of warning on 3rd party Email clients.
I’ve been hunting for a good replacement iOS email client for a long time. Airmail, Spark (both of which you mentioned), Newton and Edison all seemed to have interesting features. I actually used Spark on a test account for a trial and was very impressed.
However, after digging into the details I came across people very worried about their privacy policies and/or the actual architecture they use.
By necessity, if they offer push notifications then they require your credentials (or auth tokens) on their servers so they can determine if mail has arrived in your various accounts and also possibly during the act of collecting your mail. To be fair, those I looked at most closely are very open about this and explain how they mitigate the risk by encrypting these credentials while at rest.
However, since their services have the means to access your mail accounts independently, then there is always the possibility, however remote, that your passwords/tokens could leak out in a hack and your email security be breached. Since many services that have your banking and credit card details offer password reset by email then this is a potential problem. This also makes these companies a target for hackers.
Some of the services (I’d suggest investigating the free ones) also do analytics on your mail looking for shopping patterns and sell this data to fund the service.
Some also allow you to opt out of analytics and disable push which might be a solution, but that means you’re a couple of configuration settings away from the problem and you can’t see what’s really going on under the hood.
While I might prepared to take this risk (and I’m frequently tempted by the shiny features), this was an automatic show stopper for my job. I would literally be sharing my domain login password with a 3rd party without their consent, a sackable offence since our clients data is highly sensitive.
The only interesting 3rd party mail client I found that did not have this issue (as far as I know) is Dispatch, since it doesn’t support push - but sadly it also doesn’t support exchange, which I need.
Anyway I figured it’s best to share this since a lot of people who use these services are unaware of the issues, since they’re hardly lit in neon in the App Store.
This is broad summary of what I’ve read so If I’ve unfairly mischaracterised how any of these services work then let me know.
And of course if someone is using a secure iOS mail client with great features and exchange support then I’d like to hear about that too!