Cannot Send or Receive Emails in Apple Mail - Multiple Accounts

MacBook Pro 15" mid 2012
OSX 10.11 (El Capitan)

Cannot send or receive emails in Apple Mail.

I have three Gmail accounts and one Verizon account running through Apple Mail.

Confirmed settings with ISPs.

Been having this problem for approx 2-3 months, even with Yosemite.

Most of the day, no email. Every once in a while there is a small time of connectivity.