Speaking of Readdle, MacWord takes a quick look at Spark, their email app:

Customizable toolbar actions, contact avatars, and a sleek new look with support for Dark Mode add up to a winning update for Spark, which remains one of the best free alternatives to Apple Mail.

Another great feature is Spark’s ability to round trip PDFs sent as attachments. You can sign or annotate a PDF quickly and return it to the sender; this requires PDF Expert, however.

Spark for iOS review: Free app delivers superior mobile email experience