Emails Not Being Seen?

All of a sudden it seems my mass emails are no longer being seen?

I was alerted when people were nagging me for things i'd already told them .. when I started looking into accounts ( multiple galleries, multiple people ) it seemed none of my emails were hitting the mark.  I've asked people to search spam etc, but so many of them have honestly declared they have nothing, it has to be my end.

Any ideas?

Just to be clear, this is only when I "select all' from a gallery to mass-inform them of something ( say "prints delivered" ).  If I email an individual one-on-one, the message is seen and received.