I received an ARC of The Postmistress by Sarah Blake a few years back as part of the First Look group at BNBC. I couldn't get into it - I kept reading the first chapter because I couldn't figure out how all the characters fit together. I recently decided to read/finish that sucker, by hook or by crook, because I made a little pile of all the books that I needed to read-and-get-rid-of because they were cluttering up my office (and I felt bad that I had an ARC that I never finished).
I think what I must say about The Postmistress is that the book and I are not friends. I didn't find any of the central female characters - Iris, Emma, and Frankie - compelling, like I did Juliet and Elizabeth of The Guernsey Literary and Potato Peel Pie Society, and the male characters were lacking in direction. The timeline seemed very disjointed. I didn't like the ending; it was unsatisfying and made me grumpy.
What I did like about the book came from the long, central section about Frankie's trip through Europe as Germany sent the last of the refueee trains out of its possessions. The heartbreaking stories she recorded, people who most probably didn't survive the war, children separated from their parents. Blake highlighted the extreme difficulty Jewish refugees had in escaping Nazi persecution due to immigration laws of other countries, particularly that of the US. That central section of the book came alive for me unlike the beginning and ending.