Emails stuck in Outbox (Apple Mail)

I use Apple Mail and I have 2 email accounts (Comcast + Gmail). Most outgoing emails get stuck in Outbox. Both accounts go constantly offline. The online status states: "imap.gmail.com" on the defaults ports timed out". 

I uninstalled-reinstalled both account at least 20 times. I tried a different client email (Spark). Exact same result.

If I'm lucky, I can make 1 email go (not 2), by closing and reopening Mail. Usually by closing/opening Mail 15 times in a row, I can make 2 or 3 emails go.

Those are 2 business email accounts. It is very, very frustrating.

I tried everything I could. I'd appreciate the help. Thanks!