Emails getting "stuck" in Outbox

Many of my emails end up in outbox and they don’t send. Some are from emails I added from groups I belong to. Sometimes they send most of the time they don’t. Very frustrating. I didn’t have these issues with previous systems. I think the last upgrades are the problem but not sure.. I don’t know what to do. The outbox on my computer doesn’t show up on my phone with same unsent emails. I am so stuck on this. The email is often one I set up to do with a private group to which I belong. I don’t know what to do.

[Re-Titled by Moderator]