If Sort by Sender is no longer an option on the S5, although it was on the S3 & S4, can you suggest an email application which has this feature? I downloaded myMail, and it doesn't have that option either. I used that feature on my S3 all the time for mass email cleanup/deletion. Very convenient & I'm really going to miss it if I cannot find an application with the same capability.
That's strange - it's vanilla Android, the one that comes with Google phones. If you private message me your email address, I'll send you the apk file for version 6.0, which works with my Note 3 on KitKat (and should work on an S5).