Outlook is a decent app, I used to use it for months, but it doesn't attach as files but instead as links so it fails this topic.
Cloudmagic is in that folder too. One huge quirk Cloudmagic has is no gmail aliases so it's useless to me since my business uses aliases under one Google Apps account. Even worse is even if you add each account as an inbox you can't select the account you are responding from. Cloudmagic has been saying for a year now it would fix it or add aliases. Cloudmagic can do attachments just fine. No calendar built in like Spark or Outlook though.
Right now, Spark does it all really.
I did discover that
Spark and CloudMagic are both unfortunately also
lacking some features:
1) save multiple attachments to a cloud storage at once. I also read that this is also the case with the Mail app in iOS9 (i saw it
here)
2) option to quickly see and click the attachment(s) in an e-mail (press an attachment button to see them or press the files directly) instead of scrolling to the bottom of the e-mail to see it.
3) other languages (e.g. Dutch)
Spark other missing features:
* No iPad support
* The badge icon for a new e-mail(s) does not show, it needs background refresh turned on (wish i don't want). I don't need this for e.g. the Gmail app and Apple's Mail app and get the badge icon for new e-mail so don't understand why Spark needs it
CloudMagic other missing features:
* I also don't like the way CloudMagic currently first asks you to give access to your photos (although i wish to attach a file from GDrive or Dropbox. This only the first time when you press the attachment button when you create a new e-mail
* You also have to select e.g. Dropbox and Google Drive via a separate ... button each time to get your attachment from your cloud storage. I did get a response from CloudMagic already and they are saying that they will make the changes within a few months.
* The search features are not so great. Within Spark i managed to get recent e-mail quickly with e.g. the term 'pdf attachments'