I use K9 Mail[1] with Fastmail and I have no complaints at all.<p>1: <a href="https:&#x2F;&#x2F;f-droid.org&#x2F;repository&#x2F;browse&#x2F;?fdfilter=K9&amp;fdid=com.fsck.k9" rel="nofollow">https:&#x2F;&#x2F;f-droid.org&#x2F;repository&#x2F;browse&#x2F;?fdfilter=K9&amp;fdid=com....</a>